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 $215.62   12.789%   $243.1956   $243.20   $243.20   $243.20  
  Purchase #2 $246.36   9.171%   $268.9537   $268.95   $268.95   $269.00  
  Purchase #3 $135.92   11.486%   $151.5318   $151.53   $151.55   $151.50  
  Purchase #4 $28.57   7.871%   $30.8187   $30.82   $30.80   $30.80  
  Purchase #5 $85.90   12.216%   $96.3935   $96.39   $96.40   $96.40  
  Purchase #6 $48.37   13.766%   $55.0286   $55.03   $55.05   $55.00  
  Purchase #7 $131.83   13.235%   $149.2777   $149.28   $149.30   $149.30  
  7 purchase totals = $892.57       $995.1996   $995.20   $995.25   $995.20