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 $250.43   4.527%   $261.767   $261.77   $261.75   $261.80  
  Purchase #2 $28.68   9.107%   $31.2919   $31.29   $31.30   $31.30  
  Purchase #3 $8.75   13.688%   $9.9477   $9.95   $9.95   $9.90  
  Purchase #4 $245.77   3.547%   $254.4875   $254.49   $254.50   $254.50  
  Purchase #5 $27.48   8.251%   $29.7474   $29.75   $29.75   $29.70  
  Purchase #6 $169.77   10.269%   $187.2037   $187.20   $187.20   $187.20  
  Purchase #7 $73.39   9.432%   $80.3121   $80.31   $80.30   $80.30  
  7 purchase totals = $804.27       $854.7573   $854.76   $854.75   $854.70