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 $107.50   3.175%   $110.9131   $110.91   $110.90   $110.90  
  Purchase #2 $134.97   8.516%   $146.464   $146.46   $146.45   $146.50  
  Purchase #3 $17.93   8.306%   $19.4193   $19.42   $19.40   $19.40  
  Purchase #4 $12.55   12.447%   $14.1121   $14.11   $14.10   $14.10  
  Purchase #5 $180.30   12.707%   $203.2107   $203.21   $203.20   $203.20  
  Purchase #6 $102.42   7.632%   $110.2367   $110.24   $110.25   $110.20  
  Purchase #7 $100.50   12.718%   $113.2816   $113.28   $113.30   $113.30  
  7 purchase totals = $656.17       $717.6375   $717.63   $717.60   $717.60