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 $180.32   7.568%   $193.9666   $193.97   $193.95   $194.00  
  Purchase #2 $205.67   6.147%   $218.3125   $218.31   $218.30   $218.30  
  Purchase #3 $60.91   3.330%   $62.9383   $62.94   $62.95   $62.90  
  Purchase #4 $45.25   11.246%   $50.3388   $50.34   $50.35   $50.30  
  Purchase #5 $98.74   3.827%   $102.5188   $102.52   $102.50   $102.50  
  Purchase #6 $72.29   3.242%   $74.6336   $74.63   $74.65   $74.60  
  Purchase #7 $156.47   10.725%   $173.2514   $173.25   $173.25   $173.30  
  7 purchase totals = $819.65       $875.9600   $875.96   $875.95   $875.90