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 $184.38   9.582%   $202.0473   $202.05   $202.05   $202.00  
  Purchase #2 $224.77   5.302%   $236.6873   $236.69   $236.70   $236.70  
  Purchase #3 $153.74   8.211%   $166.3636   $166.36   $166.35   $166.40  
  Purchase #4 $211.71   11.674%   $236.425   $236.43   $236.45   $236.40  
  Purchase #5 $105.92   9.646%   $116.137   $116.14   $116.15   $116.10  
  Purchase #6 $140.61   5.744%   $148.6866   $148.69   $148.70   $148.70  
  Purchase #7 $35.95   4.179%   $37.4524   $37.45   $37.45   $37.50  
  7 purchase totals = $1,057.08       $1,143.7992   $1,143.81   $1,143.85   $1,143.80