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 $54.62   11.770%   $61.0488   $61.05   $61.05   $61.00  
  Purchase #2 $235.60   5.294%   $248.0727   $248.07   $248.05   $248.10  
  Purchase #3 $85.61   3.290%   $88.4266   $88.43   $88.45   $88.40  
  Purchase #4 $109.51   8.794%   $119.1403   $119.14   $119.15   $119.10  
  Purchase #5 $111.86   12.678%   $126.0416   $126.04   $126.05   $126.00  
  Purchase #6 $110.39   11.156%   $122.7051   $122.71   $122.70   $122.70  
  Purchase #7 $80.56   7.869%   $86.8993   $86.90   $86.90   $86.90  
  7 purchase totals = $788.15       $852.3344   $852.34   $852.35   $852.20