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 $85.78   8.126%   $92.7505   $92.75   $92.75   $92.80  
  Purchase #2 $209.41   13.431%   $237.5359   $237.54   $237.55   $237.50  
  Purchase #3 $98.86   6.346%   $105.1337   $105.13   $105.15   $105.10  
  Purchase #4 $109.71   3.765%   $113.8406   $113.84   $113.85   $113.80  
  Purchase #5 $231.91   3.401%   $239.7973   $239.80   $239.80   $239.80  
  Purchase #6 $184.56   3.564%   $191.1377   $191.14   $191.15   $191.10  
  Purchase #7 $217.41   12.582%   $244.7645   $244.76   $244.75   $244.80  
  7 purchase totals = $1,137.64       $1,224.9602   $1,224.96   $1,225.00   $1,224.90