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 $204.27   10.394%   $225.5018   $225.50   $225.50   $225.50  
  Purchase #2 $97.50   11.485%   $108.6979   $108.70   $108.70   $108.70  
  Purchase #3 $55.35   11.450%   $61.6876   $61.69   $61.70   $61.70  
  Purchase #4 $196.70   10.400%   $217.1568   $217.16   $217.15   $217.20  
  Purchase #5 $165.73   11.812%   $185.306   $185.31   $185.30   $185.30  
  Purchase #6 $55.88   4.314%   $58.2907   $58.29   $58.30   $58.30  
  Purchase #7 $65.41   6.717%   $69.8036   $69.80   $69.80   $69.80  
  7 purchase totals = $840.84       $926.4444   $926.45   $926.45   $926.50