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 $58.99   12.752%   $66.5124   $66.51   $66.50   $66.50  
  Purchase #2 $64.75   5.392%   $68.2413   $68.24   $68.25   $68.20  
  Purchase #3 $88.54   11.461%   $98.6876   $98.69   $98.70   $98.70  
  Purchase #4 $131.89   13.426%   $149.5976   $149.60   $149.60   $149.60  
  Purchase #5 $54.67   6.308%   $58.1186   $58.12   $58.10   $58.10  
  Purchase #6 $216.58   3.261%   $223.6427   $223.64   $223.65   $223.60  
  Purchase #7 $115.51   4.428%   $120.6248   $120.62   $120.60   $120.60  
  7 purchase totals = $730.93       $785.4250   $785.42   $785.40   $785.30