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 $203.69   11.483%   $227.0797   $227.08   $227.10   $227.10  
  Purchase #2 $201.93   13.552%   $229.2956   $229.30   $229.30   $229.30  
  Purchase #3 $147.42   6.107%   $156.4229   $156.42   $156.40   $156.40  
  Purchase #4 $32.37   9.639%   $35.4901   $35.49   $35.50   $35.50  
  Purchase #5 $231.37   9.495%   $253.3386   $253.34   $253.35   $253.30  
  Purchase #6 $137.90   3.302%   $142.4535   $142.45   $142.45   $142.50  
  Purchase #7 $107.32   11.762%   $119.943   $119.94   $119.95   $119.90  
  7 purchase totals = $1,062.00       $1,164.0234   $1,164.02   $1,164.05   $1,164.00