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 $232.26   9.583%   $254.5175   $254.52   $254.50   $254.50  
  Purchase #2 $31.99   7.197%   $34.2923   $34.29   $34.30   $34.30  
  Purchase #3 $110.89   6.277%   $117.8506   $117.85   $117.85   $117.90  
  Purchase #4 $24.80   3.113%   $25.572   $25.57   $25.55   $25.60  
  Purchase #5 $33.73   7.641%   $36.3073   $36.31   $36.30   $36.30  
  Purchase #6 $150.83   10.815%   $167.1423   $167.14   $167.15   $167.10  
  Purchase #7 $156.44   5.181%   $164.5452   $164.55   $164.55   $164.50  
  7 purchase totals = $740.94       $800.2272   $800.23   $800.20   $800.20