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 $216.97   4.505%   $226.7445   $226.74   $226.75   $226.70  
  Purchase #2 $92.88   3.180%   $95.8336   $95.83   $95.85   $95.80  
  Purchase #3 $207.43   7.349%   $222.674   $222.67   $222.65   $222.70  
  Purchase #4 $119.65   5.482%   $126.2092   $126.21   $126.20   $126.20  
  Purchase #5 $25.92   5.223%   $27.2738   $27.27   $27.25   $27.30  
  Purchase #6 $11.42   9.297%   $12.4817   $12.48   $12.50   $12.50  
  Purchase #7 $13.95   4.584%   $14.5895   $14.59   $14.60   $14.60  
  7 purchase totals = $688.22       $725.8063   $725.79   $725.80   $725.80