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 $59.85   10.511%   $66.1408   $66.14   $66.15   $66.10  
  Purchase #2 $247.97   13.371%   $281.1261   $281.13   $281.15   $281.10  
  Purchase #3 $146.59   6.428%   $156.0128   $156.01   $156.00   $156.00  
  Purchase #4 $7.51   6.844%   $8.024   $8.02   $8.00   $8.00  
  Purchase #5 $174.31   11.457%   $194.2807   $194.28   $194.30   $194.30  
  Purchase #6 $38.50   5.828%   $40.7438   $40.74   $40.75   $40.70  
  Purchase #7 $190.48   10.831%   $211.1109   $211.11   $211.10   $211.10  
  7 purchase totals = $865.21       $957.4391   $957.43   $957.45   $957.30