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 $54.87   10.685%   $60.7329   $60.73   $60.75   $60.70  
  Purchase #2 $144.95   4.560%   $151.5597   $151.56   $151.55   $151.60  
  Purchase #3 $200.37   12.435%   $225.286   $225.29   $225.30   $225.30  
  Purchase #4 $53.90   11.659%   $60.1842   $60.18   $60.20   $60.20  
  Purchase #5 $192.37   13.824%   $218.9632   $218.96   $218.95   $219.00  
  Purchase #6 $77.94   11.794%   $87.1322   $87.13   $87.15   $87.10  
  Purchase #7 $159.67   13.368%   $181.0147   $181.01   $181.00   $181.00  
  7 purchase totals = $884.07       $984.8729   $984.86   $984.90   $984.90