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 $59.84   8.595%   $64.9832   $64.98   $65.00   $65.00  
  Purchase #2 $155.32   9.644%   $170.2991   $170.30   $170.30   $170.30  
  Purchase #3 $202.71   9.273%   $221.5073   $221.51   $221.50   $221.50  
  Purchase #4 $146.62   10.497%   $162.0107   $162.01   $162.00   $162.00  
  Purchase #5 $133.57   5.142%   $140.4382   $140.44   $140.45   $140.40  
  Purchase #6 $93.55   5.122%   $98.3416   $98.34   $98.35   $98.30  
  Purchase #7 $139.49   4.822%   $146.2162   $146.22   $146.20   $146.20  
  7 purchase totals = $931.10       $1,003.7963   $1,003.80   $1,003.80   $1,003.70