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 $60.94   13.791%   $69.3442   $69.34   $69.35   $69.30  
  Purchase #2 $9.64   7.409%   $10.3542   $10.35   $10.35   $10.40  
  Purchase #3 $59.35   11.385%   $66.107   $66.11   $66.10   $66.10  
  Purchase #4 $26.85   7.730%   $28.9255   $28.93   $28.95   $28.90  
  Purchase #5 $247.73   11.745%   $276.8259   $276.83   $276.85   $276.80  
  Purchase #6 $232.72   9.620%   $255.1077   $255.11   $255.10   $255.10  
  Purchase #7 $53.49   5.842%   $56.6149   $56.61   $56.60   $56.60  
  7 purchase totals = $690.72       $763.2794   $763.28   $763.30   $763.20