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 $94.26   10.646%   $104.2949   $104.29   $104.30   $104.30  
  Purchase #2 $195.43   12.443%   $219.7474   $219.75   $219.75   $219.70  
  Purchase #3 $18.44   3.654%   $19.1138   $19.11   $19.10   $19.10  
  Purchase #4 $116.84   5.336%   $123.0746   $123.07   $123.05   $123.10  
  Purchase #5 $136.74   10.452%   $151.0321   $151.03   $151.05   $151.00  
  Purchase #6 $65.91   11.314%   $73.3671   $73.37   $73.35   $73.40  
  Purchase #7 $210.73   10.405%   $232.6565   $232.66   $232.65   $232.70  
  7 purchase totals = $838.35       $923.2864   $923.28   $923.25   $923.30