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 $14.81   6.754%   $15.8103   $15.81   $15.80   $15.80  
  Purchase #2 $169.45   10.712%   $187.6015   $187.60   $187.60   $187.60  
  Purchase #3 $10.33   9.235%   $11.284   $11.28   $11.30   $11.30  
  Purchase #4 $28.88   12.633%   $32.5284   $32.53   $32.55   $32.50  
  Purchase #5 $143.79   5.369%   $151.5101   $151.51   $151.50   $151.50  
  Purchase #6 $212.91   6.443%   $226.6278   $226.63   $226.65   $226.60  
  Purchase #7 $126.75   5.718%   $133.9976   $134.00   $134.00   $134.00  
  7 purchase totals = $706.92       $759.3597   $759.36   $759.40   $759.30