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 $214.40   7.667%   $230.838   $230.84   $230.85   $230.80  
  Purchase #2 $241.58   5.626%   $255.1713   $255.17   $255.15   $255.20  
  Purchase #3 $34.91   7.594%   $37.5611   $37.56   $37.55   $37.60  
  Purchase #4 $112.43   3.821%   $116.726   $116.73   $116.75   $116.70  
  Purchase #5 $36.76   12.295%   $41.2796   $41.28   $41.30   $41.30  
  Purchase #6 $12.89   10.557%   $14.2508   $14.25   $14.25   $14.30  
  Purchase #7 $70.65   3.600%   $73.1934   $73.19   $73.20   $73.20  
  7 purchase totals = $723.62       $769.0202   $769.02   $769.05   $769.10