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 $208.97   12.408%   $234.899   $234.90   $234.90   $234.90  
  Purchase #2 $243.83   13.779%   $277.4273   $277.43   $277.45   $277.40  
  Purchase #3 $182.65   4.275%   $190.4583   $190.46   $190.45   $190.50  
  Purchase #4 $227.33   6.687%   $242.5316   $242.53   $242.55   $242.50  
  Purchase #5 $85.66   3.575%   $88.7223   $88.72   $88.70   $88.70  
  Purchase #6 $103.87   3.542%   $107.5491   $107.55   $107.55   $107.50  
  Purchase #7 $196.57   6.281%   $208.9166   $208.92   $208.90   $208.90  
  7 purchase totals = $1,248.88       $1,350.5042   $1,350.51   $1,350.50   $1,350.40