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 $52.78   13.170%   $59.7311   $59.73   $59.75   $59.70  
  Purchase #2 $181.85   6.850%   $194.3067   $194.31   $194.30   $194.30  
  Purchase #3 $86.70   12.653%   $97.6702   $97.67   $97.65   $97.70  
  Purchase #4 $99.39   7.712%   $107.055   $107.06   $107.05   $107.10  
  Purchase #5 $69.99   3.437%   $72.3956   $72.40   $72.40   $72.40  
  Purchase #6 $119.40   11.564%   $133.2074   $133.21   $133.20   $133.20  
  Purchase #7 $76.72   6.685%   $81.8487   $81.85   $81.85   $81.80  
  7 purchase totals = $686.83       $746.2147   $746.23   $746.20   $746.20