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 $51.64   12.798%   $58.2489   $58.25   $58.25   $58.20  
  Purchase #2 $132.31   12.347%   $148.6463   $148.65   $148.65   $148.60  
  Purchase #3 $113.80   13.178%   $128.7966   $128.80   $128.80   $128.80  
  Purchase #4 $53.48   4.624%   $55.9529   $55.95   $55.95   $56.00  
  Purchase #5 $9.76   11.809%   $10.9126   $10.91   $10.90   $10.90  
  Purchase #6 $155.44   8.327%   $168.3835   $168.38   $168.40   $168.40  
  Purchase #7 $155.52   6.277%   $165.282   $165.28   $165.30   $165.30  
  7 purchase totals = $671.95       $736.2228   $736.22   $736.25   $736.20