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 $91.53   11.711%   $102.2491   $102.25   $102.25   $102.20  
  Purchase #2 $51.53   5.237%   $54.2286   $54.23   $54.25   $54.20  
  Purchase #3 $62.50   13.759%   $71.0994   $71.10   $71.10   $71.10  
  Purchase #4 $104.78   11.182%   $116.4965   $116.50   $116.50   $116.50  
  Purchase #5 $20.34   9.280%   $22.2276   $22.23   $22.25   $22.20  
  Purchase #6 $58.82   3.793%   $61.051   $61.05   $61.05   $61.10  
  Purchase #7 $188.45   5.646%   $199.0899   $199.09   $199.10   $199.10  
  7 purchase totals = $577.95       $626.4421   $626.45   $626.50   $626.40