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 $71.39   7.222%   $76.5458   $76.55   $76.55   $76.50  
  Purchase #2 $61.39   8.645%   $66.6972   $66.70   $66.70   $66.70  
  Purchase #3 $38.93   13.568%   $44.212   $44.21   $44.20   $44.20  
  Purchase #4 $245.62   10.812%   $272.1764   $272.18   $272.20   $272.20  
  Purchase #5 $205.26   5.700%   $216.9598   $216.96   $216.95   $217.00  
  Purchase #6 $123.69   7.593%   $133.0818   $133.08   $133.10   $133.10  
  Purchase #7 $233.87   11.430%   $260.6013   $260.60   $260.60   $260.60  
  7 purchase totals = $980.15       $1,070.2743   $1,070.28   $1,070.30   $1,070.30