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 $174.43   8.730%   $189.6577   $189.66   $189.65   $189.70  
  Purchase #2 $206.39   6.601%   $220.0138   $220.01   $220.00   $220.00  
  Purchase #3 $118.90   10.818%   $131.7626   $131.76   $131.75   $131.80  
  Purchase #4 $170.56   13.699%   $193.925   $193.93   $193.95   $193.90  
  Purchase #5 $240.86   13.795%   $274.0866   $274.09   $274.10   $274.10  
  Purchase #6 $198.47   6.556%   $211.4817   $211.48   $211.50   $211.50  
  Purchase #7 $226.80   6.685%   $241.9616   $241.96   $241.95   $242.00  
  7 purchase totals = $1,336.41       $1,462.8890   $1,462.89   $1,462.90   $1,463.00