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 $83.82   10.468%   $92.5943   $92.59   $92.60   $92.60  
  Purchase #2 $208.74   11.609%   $232.9726   $232.97   $232.95   $233.00  
  Purchase #3 $13.35   12.575%   $15.0288   $15.03   $15.05   $15.00  
  Purchase #4 $202.86   8.341%   $219.7806   $219.78   $219.80   $219.80  
  Purchase #5 $84.55   5.870%   $89.5131   $89.51   $89.50   $89.50  
  Purchase #6 $246.36   13.576%   $279.8058   $279.81   $279.80   $279.80  
  Purchase #7 $203.51   6.577%   $216.8949   $216.89   $216.90   $216.90  
  7 purchase totals = $1,043.19       $1,146.5901   $1,146.58   $1,146.60   $1,146.60