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 $62.81   4.722%   $65.7759   $65.78   $65.80   $65.80  
  Purchase #2 $67.74   10.568%   $74.8988   $74.90   $74.90   $74.90  
  Purchase #3 $37.45   11.557%   $41.7781   $41.78   $41.80   $41.80  
  Purchase #4 $204.63   12.272%   $229.7422   $229.74   $229.75   $229.70  
  Purchase #5 $81.25   4.186%   $84.6511   $84.65   $84.65   $84.70  
  Purchase #6 $92.71   6.461%   $98.7   $98.70   $98.70   $98.70  
  Purchase #7 $174.64   12.466%   $196.4106   $196.41   $196.40   $196.40  
  7 purchase totals = $721.23       $791.9567   $791.96   $792.00   $792.00