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 $152.44   13.856%   $173.5621   $173.56   $173.55   $173.60  
  Purchase #2 $223.91   11.161%   $248.9006   $248.90   $248.90   $248.90  
  Purchase #3 $151.60   6.671%   $161.7132   $161.71   $161.70   $161.70  
  Purchase #4 $212.62   9.423%   $232.6552   $232.66   $232.65   $232.70  
  Purchase #5 $188.27   6.452%   $200.4172   $200.42   $200.40   $200.40  
  Purchase #6 $125.68   3.424%   $129.9833   $129.98   $130.00   $130.00  
  Purchase #7 $229.63   7.610%   $247.1048   $247.10   $247.10   $247.10  
  7 purchase totals = $1,284.15       $1,394.3364   $1,394.33   $1,394.30   $1,394.40