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 $64.68   13.405%   $73.3504   $73.35   $73.35   $73.40  
  Purchase #2 $100.73   9.534%   $110.3336   $110.33   $110.35   $110.30  
  Purchase #3 $219.42   12.316%   $246.4438   $246.44   $246.45   $246.40  
  Purchase #4 $74.68   4.376%   $77.948   $77.95   $77.95   $77.90  
  Purchase #5 $106.57   9.382%   $116.5684   $116.57   $116.55   $116.60  
  Purchase #6 $151.67   7.190%   $162.5751   $162.58   $162.60   $162.60  
  Purchase #7 $130.44   5.771%   $137.9677   $137.97   $137.95   $138.00  
  7 purchase totals = $848.19       $925.1870   $925.19   $925.20   $925.20