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 $191.85   7.518%   $206.2733   $206.27   $206.25   $206.30  
  Purchase #2 $86.27   11.118%   $95.8615   $95.86   $95.85   $95.90  
  Purchase #3 $220.97   3.643%   $229.0199   $229.02   $229.00   $229.00  
  Purchase #4 $153.55   11.860%   $171.761   $171.76   $171.75   $171.80  
  Purchase #5 $34.47   8.527%   $37.4093   $37.41   $37.40   $37.40  
  Purchase #6 $128.46   13.428%   $145.7096   $145.71   $145.70   $145.70  
  Purchase #7 $67.38   11.719%   $75.2763   $75.28   $75.30   $75.30  
  7 purchase totals = $882.95       $961.3109   $961.31   $961.25   $961.40