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 $182.71   8.140%   $197.5826   $197.58   $197.60   $197.60  
  Purchase #2 $219.25   12.157%   $245.9042   $245.90   $245.90   $245.90  
  Purchase #3 $120.86   8.862%   $131.5706   $131.57   $131.55   $131.60  
  Purchase #4 $240.39   9.246%   $262.6165   $262.62   $262.60   $262.60  
  Purchase #5 $18.55   9.201%   $20.2568   $20.26   $20.25   $20.30  
  Purchase #6 $163.31   3.798%   $169.5125   $169.51   $169.50   $169.50  
  Purchase #7 $182.45   11.426%   $203.2967   $203.30   $203.30   $203.30  
  7 purchase totals = $1,127.52       $1,230.7399   $1,230.74   $1,230.70   $1,230.80