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 $184.41   5.258%   $194.1063   $194.11   $194.10   $194.10  
  Purchase #2 $149.49   12.373%   $167.9864   $167.99   $168.00   $168.00  
  Purchase #3 $121.50   9.187%   $132.6622   $132.66   $132.65   $132.70  
  Purchase #4 $26.88   10.321%   $29.6543   $29.65   $29.65   $29.70  
  Purchase #5 $72.84   8.265%   $78.8602   $78.86   $78.85   $78.90  
  Purchase #6 $200.71   4.452%   $209.6456   $209.65   $209.65   $209.60  
  Purchase #7 $8.85   6.316%   $9.409   $9.41   $9.40   $9.40  
  7 purchase totals = $764.68       $822.3240   $822.33   $822.30   $822.40