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 $56.46   7.170%   $60.5082   $60.51   $60.50   $60.50  
  Purchase #2 $94.60   4.279%   $98.6479   $98.65   $98.65   $98.60  
  Purchase #3 $29.59   10.388%   $32.6638   $32.66   $32.65   $32.70  
  Purchase #4 $79.42   8.198%   $85.9309   $85.93   $85.95   $85.90  
  Purchase #5 $24.76   10.339%   $27.3199   $27.32   $27.30   $27.30  
  Purchase #6 $218.59   6.354%   $232.4792   $232.48   $232.50   $232.50  
  Purchase #7 $181.67   12.279%   $203.9773   $203.98   $204.00   $204.00  
  7 purchase totals = $685.09       $741.5272   $741.53   $741.55   $741.50