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 $223.83   8.669%   $243.2338   $243.23   $243.25   $243.20  
  Purchase #2 $203.78   6.159%   $216.3308   $216.33   $216.35   $216.30  
  Purchase #3 $211.88   5.377%   $223.2728   $223.27   $223.25   $223.30  
  Purchase #4 $130.78   3.828%   $135.7863   $135.79   $135.80   $135.80  
  Purchase #5 $129.42   5.445%   $136.4669   $136.47   $136.45   $136.50  
  Purchase #6 $131.71   11.529%   $146.8948   $146.89   $146.90   $146.90  
  Purchase #7 $159.41   4.765%   $167.0059   $167.01   $167.00   $167.00  
  7 purchase totals = $1,190.81       $1,268.9913   $1,268.99   $1,269.00   $1,269.00