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 $192.76   6.324%   $204.9501   $204.95   $204.95   $205.00  
  Purchase #2 $243.29   13.341%   $275.7473   $275.75   $275.75   $275.70  
  Purchase #3 $56.34   13.862%   $64.1499   $64.15   $64.15   $64.10  
  Purchase #4 $140.61   6.767%   $150.1251   $150.13   $150.15   $150.10  
  Purchase #5 $60.34   7.221%   $64.6972   $64.70   $64.70   $64.70  
  Purchase #6 $226.75   4.207%   $236.2894   $236.29   $236.30   $236.30  
  Purchase #7 $12.81   3.233%   $13.2241   $13.22   $13.20   $13.20  
  7 purchase totals = $932.90       $1,009.1831   $1,009.19   $1,009.20   $1,009.10