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 $29.55   10.177%   $32.5573   $32.56   $32.55   $32.60  
  Purchase #2 $49.91   8.415%   $54.1099   $54.11   $54.10   $54.10  
  Purchase #3 $59.37   10.816%   $65.7915   $65.79   $65.80   $65.80  
  Purchase #4 $241.78   3.369%   $249.9256   $249.93   $249.95   $249.90  
  Purchase #5 $245.34   13.808%   $279.2165   $279.22   $279.20   $279.20  
  Purchase #6 $33.83   6.351%   $35.9785   $35.98   $36.00   $36.00  
  Purchase #7 $238.48   12.126%   $267.3981   $267.40   $267.40   $267.40  
  7 purchase totals = $898.26       $984.9774   $984.99   $985.00   $985.00