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 $83.96   11.545%   $93.6532   $93.65   $93.65   $93.70  
  Purchase #2 $89.46   11.412%   $99.6692   $99.67   $99.65   $99.70  
  Purchase #3 $107.85   12.751%   $121.602   $121.60   $121.60   $121.60  
  Purchase #4 $22.85   9.693%   $25.0649   $25.06   $25.05   $25.10  
  Purchase #5 $195.74   3.404%   $202.403   $202.40   $202.40   $202.40  
  Purchase #6 $78.83   13.445%   $89.4287   $89.43   $89.45   $89.40  
  Purchase #7 $217.49   5.427%   $229.2932   $229.29   $229.30   $229.30  
  7 purchase totals = $796.18       $861.1142   $861.10   $861.10   $861.20