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 $195.41   3.846%   $202.9255   $202.93   $202.95   $202.90  
  Purchase #2 $64.99   3.646%   $67.3595   $67.36   $67.35   $67.40  
  Purchase #3 $164.25   12.301%   $184.4544   $184.45   $184.45   $184.50  
  Purchase #4 $229.98   13.400%   $260.7973   $260.80   $260.80   $260.80  
  Purchase #5 $63.29   12.605%   $71.2677   $71.27   $71.25   $71.30  
  Purchase #6 $34.73   5.654%   $36.6936   $36.69   $36.70   $36.70  
  Purchase #7 $123.39   5.378%   $130.0259   $130.03   $130.05   $130.00  
  7 purchase totals = $876.04       $953.5239   $953.53   $953.55   $953.60