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 $87.90   6.197%   $93.3472   $93.35   $93.35   $93.30  
  Purchase #2 $141.90   3.695%   $147.1432   $147.14   $147.15   $147.10  
  Purchase #3 $174.64   5.664%   $184.5316   $184.53   $184.55   $184.50  
  Purchase #4 $23.50   6.359%   $24.9944   $24.99   $25.00   $25.00  
  Purchase #5 $140.47   8.448%   $152.3369   $152.34   $152.35   $152.30  
  Purchase #6 $94.89   5.215%   $99.8385   $99.84   $99.85   $99.80  
  Purchase #7 $59.93   9.686%   $65.7348   $65.73   $65.75   $65.70  
  7 purchase totals = $723.23       $767.9266   $767.92   $768.00   $767.70