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 $33.99   9.383%   $37.1793   $37.18   $37.20   $37.20  
  Purchase #2 $217.36   12.207%   $243.8931   $243.89   $243.90   $243.90  
  Purchase #3 $158.92   12.126%   $178.1906   $178.19   $178.20   $178.20  
  Purchase #4 $118.43   7.131%   $126.8752   $126.88   $126.90   $126.90  
  Purchase #5 $28.96   12.772%   $32.6588   $32.66   $32.65   $32.70  
  Purchase #6 $226.73   13.181%   $256.6153   $256.62   $256.60   $256.60  
  Purchase #7 $141.71   4.313%   $147.822   $147.82   $147.80   $147.80  
  7 purchase totals = $926.10       $1,023.2343   $1,023.24   $1,023.25   $1,023.30