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 $61.55   11.121%   $68.395   $68.40   $68.40   $68.40  
  Purchase #2 $200.88   12.599%   $226.1889   $226.19   $226.20   $226.20  
  Purchase #3 $48.85   6.289%   $51.9222   $51.92   $51.90   $51.90  
  Purchase #4 $67.79   4.679%   $70.9619   $70.96   $70.95   $71.00  
  Purchase #5 $250.91   10.140%   $276.3523   $276.35   $276.35   $276.40  
  Purchase #6 $133.37   7.191%   $142.9606   $142.96   $142.95   $143.00  
  Purchase #7 $116.75   4.138%   $121.5811   $121.58   $121.60   $121.60  
  7 purchase totals = $880.10       $958.3620   $958.36   $958.35   $958.50