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 $61.37   8.466%   $66.5656   $66.57   $66.55   $66.60  
  Purchase #2 $229.96   5.369%   $242.3066   $242.31   $242.30   $242.30  
  Purchase #3 $122.90   5.603%   $129.7861   $129.79   $129.80   $129.80  
  Purchase #4 $84.47   7.434%   $90.7495   $90.75   $90.75   $90.70  
  Purchase #5 $46.96   12.679%   $52.9141   $52.91   $52.90   $52.90  
  Purchase #6 $184.43   5.347%   $194.2915   $194.29   $194.30   $194.30  
  Purchase #7 $179.27   6.462%   $190.8544   $190.85   $190.85   $190.90  
  7 purchase totals = $909.36       $967.4678   $967.47   $967.45   $967.50