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 $144.99   4.496%   $151.5088   $151.51   $151.50   $151.50  
  Purchase #2 $184.27   11.760%   $205.9402   $205.94   $205.95   $205.90  
  Purchase #3 $115.84   8.495%   $125.6806   $125.68   $125.70   $125.70  
  Purchase #4 $87.73   4.114%   $91.3392   $91.34   $91.35   $91.30  
  Purchase #5 $208.44   11.272%   $231.9354   $231.94   $231.95   $231.90  
  Purchase #6 $150.95   10.674%   $167.0624   $167.06   $167.05   $167.10  
  Purchase #7 $233.83   8.578%   $253.8879   $253.89   $253.90   $253.90  
  7 purchase totals = $1,126.05       $1,227.3545   $1,227.36   $1,227.40   $1,227.30