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 $218.79   3.192%   $225.7738   $225.77   $225.75   $225.80  
  Purchase #2 $157.89   10.143%   $173.9048   $173.90   $173.90   $173.90  
  Purchase #3 $85.27   8.572%   $92.5793   $92.58   $92.60   $92.60  
  Purchase #4 $212.81   7.391%   $228.5388   $228.54   $228.55   $228.50  
  Purchase #5 $25.82   11.460%   $28.779   $28.78   $28.80   $28.80  
  Purchase #6 $225.68   5.730%   $238.6115   $238.61   $238.60   $238.60  
  Purchase #7 $20.47   9.802%   $22.4765   $22.48   $22.50   $22.50  
  7 purchase totals = $946.73       $1,010.6637   $1,010.66   $1,010.70   $1,010.70