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 $86.29   11.294%   $96.0356   $96.04   $96.05   $96.00  
  Purchase #2 $249.31   8.149%   $269.6263   $269.63   $269.65   $269.60  
  Purchase #3 $133.51   5.636%   $141.0346   $141.03   $141.05   $141.00  
  Purchase #4 $145.93   5.366%   $153.7606   $153.76   $153.75   $153.80  
  Purchase #5 $32.75   8.589%   $35.5629   $35.56   $35.55   $35.60  
  Purchase #6 $227.78   12.265%   $255.7172   $255.72   $255.70   $255.70  
  Purchase #7 $117.40   13.399%   $133.1304   $133.13   $133.15   $133.10  
  7 purchase totals = $992.97       $1,084.8676   $1,084.87   $1,084.90   $1,084.80