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 $241.81   9.609%   $265.0455   $265.05   $265.05   $265.00  
  Purchase #2 $201.91   13.143%   $228.447   $228.45   $228.45   $228.40  
  Purchase #3 $173.52   10.229%   $191.2694   $191.27   $191.25   $191.30  
  Purchase #4 $218.99   10.297%   $241.5394   $241.54   $241.55   $241.50  
  Purchase #5 $59.49   10.110%   $65.5044   $65.50   $65.50   $65.50  
  Purchase #6 $22.76   3.781%   $23.6206   $23.62   $23.60   $23.60  
  Purchase #7 $209.66   12.539%   $235.9493   $235.95   $235.95   $235.90  
  7 purchase totals = $1,128.14       $1,251.3756   $1,251.38   $1,251.35   $1,251.20