Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $247.83   10.695%   $274.3354   $274.34   $274.35   $274.30  
  Purchase #2 $156.77   12.809%   $176.8507   $176.85   $176.85   $176.90  
  Purchase #3 $241.80   4.651%   $253.0461   $253.05   $253.05   $253.00  
  Purchase #4 $95.78   10.540%   $105.8752   $105.88   $105.90   $105.90  
  Purchase #5 $176.82   9.476%   $193.5755   $193.58   $193.60   $193.60  
  Purchase #6 $218.78   3.371%   $226.1551   $226.16   $226.15   $226.20  
  Purchase #7 $182.98   11.483%   $203.9916   $203.99   $204.00   $204.00  
  7 purchase totals = $1,320.76       $1,433.8296   $1,433.85   $1,433.90   $1,433.90