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 $89.67   3.597%   $92.8954   $92.90   $92.90   $92.90  
  Purchase #2 $150.74   13.769%   $171.4954   $171.50   $171.50   $171.50  
  Purchase #3 $71.57   5.422%   $75.4505   $75.45   $75.45   $75.50  
  Purchase #4 $162.81   6.836%   $173.9397   $173.94   $173.95   $173.90  
  Purchase #5 $202.85   6.620%   $216.2787   $216.28   $216.30   $216.30  
  Purchase #6 $47.95   13.243%   $54.3   $54.30   $54.30   $54.30  
  Purchase #7 $176.91   13.793%   $201.3112   $201.31   $201.30   $201.30  
  7 purchase totals = $902.50       $985.6709   $985.68   $985.70   $985.70