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 $67.84   9.838%   $74.5141   $74.51   $74.50   $74.50  
  Purchase #2 $94.77   13.818%   $107.8653   $107.87   $107.85   $107.90  
  Purchase #3 $91.62   10.710%   $101.4325   $101.43   $101.45   $101.40  
  Purchase #4 $220.28   7.309%   $236.3803   $236.38   $236.40   $236.40  
  Purchase #5 $205.62   9.655%   $225.4726   $225.47   $225.45   $225.50  
  Purchase #6 $240.85   11.637%   $268.8777   $268.88   $268.90   $268.90  
  Purchase #7 $207.25   3.151%   $213.7804   $213.78   $213.80   $213.80  
  7 purchase totals = $1,128.23       $1,228.3229   $1,228.32   $1,228.35   $1,228.40