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 $70.38   8.814%   $76.5833   $76.58   $76.60   $76.60  
  Purchase #2 $200.40   13.266%   $226.9851   $226.99   $227.00   $227.00  
  Purchase #3 $72.39   6.850%   $77.3487   $77.35   $77.35   $77.30  
  Purchase #4 $167.84   6.804%   $179.2598   $179.26   $179.25   $179.30  
  Purchase #5 $236.57   6.676%   $252.3634   $252.36   $252.35   $252.40  
  Purchase #6 $194.53   3.850%   $202.0194   $202.02   $202.00   $202.00  
  Purchase #7 $237.49   7.866%   $256.171   $256.17   $256.15   $256.20  
  7 purchase totals = $1,179.60       $1,270.7307   $1,270.73   $1,270.70   $1,270.80