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 $23.73   3.694%   $24.6066   $24.61   $24.60   $24.60  
  Purchase #2 $243.64   7.763%   $262.5538   $262.55   $262.55   $262.60  
  Purchase #3 $42.55   6.585%   $45.3519   $45.35   $45.35   $45.40  
  Purchase #4 $116.94   4.776%   $122.5251   $122.53   $122.55   $122.50  
  Purchase #5 $106.25   10.690%   $117.6081   $117.61   $117.60   $117.60  
  Purchase #6 $245.57   9.241%   $268.2631   $268.26   $268.25   $268.30  
  Purchase #7 $145.74   4.511%   $152.3143   $152.31   $152.30   $152.30  
  7 purchase totals = $924.42       $993.2229   $993.22   $993.20   $993.30