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 $33.83   5.604%   $35.7258   $35.73   $35.75   $35.70  
  Purchase #2 $195.46   4.777%   $204.7971   $204.80   $204.80   $204.80  
  Purchase #3 $109.44   8.852%   $119.1276   $119.13   $119.15   $119.10  
  Purchase #4 $171.71   7.505%   $184.5968   $184.60   $184.60   $184.60  
  Purchase #5 $42.51   9.503%   $46.5497   $46.55   $46.55   $46.50  
  Purchase #6 $49.36   9.324%   $53.9623   $53.96   $53.95   $54.00  
  Purchase #7 $70.98   10.864%   $78.6913   $78.69   $78.70   $78.70  
  7 purchase totals = $673.29       $723.4506   $723.46   $723.50   $723.40