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 $101.53   11.799%   $113.5095   $113.51   $113.50   $113.50  
  Purchase #2 $215.67   6.250%   $229.1494   $229.15   $229.15   $229.10  
  Purchase #3 $179.58   13.516%   $203.852   $203.85   $203.85   $203.90  
  Purchase #4 $214.54   8.302%   $232.3511   $232.35   $232.35   $232.40  
  Purchase #5 $184.27   5.261%   $193.9644   $193.96   $193.95   $194.00  
  Purchase #6 $14.79   6.693%   $15.7799   $15.78   $15.80   $15.80  
  Purchase #7 $64.58   13.256%   $73.1407   $73.14   $73.15   $73.10  
  7 purchase totals = $974.96       $1,061.7470   $1,061.74   $1,061.75   $1,061.80