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 $66.26   10.681%   $73.3372   $73.34   $73.35   $73.30  
  Purchase #2 $110.50   9.172%   $120.6351   $120.64   $120.65   $120.60  
  Purchase #3 $152.48   5.458%   $160.8024   $160.80   $160.80   $160.80  
  Purchase #4 $26.36   8.587%   $28.6235   $28.62   $28.60   $28.60  
  Purchase #5 $210.47   10.267%   $232.079   $232.08   $232.10   $232.10  
  Purchase #6 $109.85   5.560%   $115.9577   $115.96   $115.95   $116.00  
  Purchase #7 $145.47   4.766%   $152.4031   $152.40   $152.40   $152.40  
  7 purchase totals = $821.39       $883.8380   $883.84   $883.85   $883.80