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 $10.94   5.746%   $11.5686   $11.57   $11.55   $11.60  
  Purchase #2 $32.35   13.439%   $36.6975   $36.70   $36.70   $36.70  
  Purchase #3 $61.90   4.394%   $64.6199   $64.62   $64.60   $64.60  
  Purchase #4 $219.73   7.538%   $236.2932   $236.29   $236.30   $236.30  
  Purchase #5 $37.53   7.177%   $40.2235   $40.22   $40.20   $40.20  
  Purchase #6 $82.69   6.714%   $88.2418   $88.24   $88.25   $88.20  
  Purchase #7 $174.82   13.841%   $199.0168   $199.02   $199.00   $199.00  
  7 purchase totals = $619.96       $676.6613   $676.66   $676.60   $676.60