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 $204.49   9.110%   $223.119   $223.12   $223.10   $223.10  
  Purchase #2 $231.42   5.277%   $243.632   $243.63   $243.65   $243.60  
  Purchase #3 $51.31   7.687%   $55.2542   $55.25   $55.25   $55.30  
  Purchase #4 $194.73   8.677%   $211.6267   $211.63   $211.65   $211.60  
  Purchase #5 $158.79   4.638%   $166.1547   $166.15   $166.15   $166.20  
  Purchase #6 $234.87   10.805%   $260.2477   $260.25   $260.25   $260.20  
  Purchase #7 $113.70   9.523%   $124.5277   $124.53   $124.55   $124.50  
  7 purchase totals = $1,189.31       $1,284.5620   $1,284.56   $1,284.60   $1,284.50