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 $91.76   13.578%   $104.2192   $104.22   $104.20   $104.20  
  Purchase #2 $241.97   10.454%   $267.2655   $267.27   $267.25   $267.30  
  Purchase #3 $164.31   11.331%   $182.928   $182.93   $182.95   $182.90  
  Purchase #4 $190.32   10.267%   $209.8602   $209.86   $209.85   $209.90  
  Purchase #5 $78.30   13.487%   $88.8603   $88.86   $88.85   $88.90  
  Purchase #6 $226.93   3.764%   $235.4716   $235.47   $235.45   $235.50  
  Purchase #7 $155.69   13.794%   $177.1659   $177.17   $177.15   $177.20  
  7 purchase totals = $1,149.28       $1,265.7707   $1,265.78   $1,265.70   $1,265.90