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 $172.54   12.572%   $194.2317   $194.23   $194.25   $194.20  
  Purchase #2 $226.92   7.493%   $243.9231   $243.92   $243.90   $243.90  
  Purchase #3 $160.91   4.226%   $167.7101   $167.71   $167.70   $167.70  
  Purchase #4 $180.30   3.808%   $187.1658   $187.17   $187.15   $187.20  
  Purchase #5 $32.76   9.445%   $35.8542   $35.85   $35.85   $35.90  
  Purchase #6 $247.66   8.403%   $268.4709   $268.47   $268.45   $268.50  
  Purchase #7 $226.63   13.182%   $256.5044   $256.50   $256.50   $256.50  
  7 purchase totals = $1,247.72       $1,353.8602   $1,353.85   $1,353.80   $1,353.90