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 $205.81   4.277%   $214.6125   $214.61   $214.60   $214.60  
  Purchase #2 $186.40   13.306%   $211.2024   $211.20   $211.20   $211.20  
  Purchase #3 $95.65   4.254%   $99.719   $99.72   $99.70   $99.70  
  Purchase #4 $221.79   4.506%   $231.7839   $231.78   $231.80   $231.80  
  Purchase #5 $235.42   12.680%   $265.2713   $265.27   $265.25   $265.30  
  Purchase #6 $28.33   4.596%   $29.632   $29.63   $29.65   $29.60  
  Purchase #7 $91.84   11.695%   $102.5807   $102.58   $102.60   $102.60  
  7 purchase totals = $1,065.24       $1,154.8018   $1,154.79   $1,154.80   $1,154.80