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 $116.64   13.140%   $131.9665   $131.97   $131.95   $132.00  
  Purchase #2 $68.56   8.360%   $74.2916   $74.29   $74.30   $74.30  
  Purchase #3 $137.64   13.829%   $156.6742   $156.67   $156.65   $156.70  
  Purchase #4 $105.51   10.807%   $116.9125   $116.91   $116.90   $116.90  
  Purchase #5 $153.94   3.578%   $159.448   $159.45   $159.45   $159.40  
  Purchase #6 $74.43   9.462%   $81.4726   $81.47   $81.45   $81.50  
  Purchase #7 $211.25   9.728%   $231.8004   $231.80   $231.80   $231.80  
  7 purchase totals = $867.97       $952.5658   $952.56   $952.50   $952.60