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 $217.53   4.226%   $226.7228   $226.72   $226.70   $226.70  
  Purchase #2 $240.92   10.255%   $265.6263   $265.63   $265.65   $265.60  
  Purchase #3 $147.73   9.548%   $161.8353   $161.84   $161.85   $161.80  
  Purchase #4 $164.95   9.804%   $181.1217   $181.12   $181.10   $181.10  
  Purchase #5 $118.51   10.124%   $130.508   $130.51   $130.50   $130.50  
  Purchase #6 $205.40   13.609%   $233.3529   $233.35   $233.35   $233.40  
  Purchase #7 $243.37   7.700%   $262.1095   $262.11   $262.10   $262.10  
  7 purchase totals = $1,338.41       $1,461.2765   $1,461.28   $1,461.25   $1,461.20