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 $199.93   5.654%   $211.234   $211.23   $211.25   $211.20  
  Purchase #2 $50.63   12.127%   $56.7699   $56.77   $56.75   $56.80  
  Purchase #3 $224.61   8.376%   $243.4233   $243.42   $243.40   $243.40  
  Purchase #4 $242.61   6.263%   $257.8047   $257.80   $257.80   $257.80  
  Purchase #5 $204.91   5.355%   $215.8829   $215.88   $215.90   $215.90  
  Purchase #6 $93.91   6.277%   $99.8047   $99.80   $99.80   $99.80  
  Purchase #7 $157.67   8.712%   $171.4062   $171.41   $171.40   $171.40  
  7 purchase totals = $1,174.27       $1,256.3257   $1,256.31   $1,256.30   $1,256.30