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 $29.90   7.261%   $32.071   $32.07   $32.05   $32.10  
  Purchase #2 $105.89   4.587%   $110.7472   $110.75   $110.75   $110.70  
  Purchase #3 $80.65   7.110%   $86.3842   $86.38   $86.40   $86.40  
  Purchase #4 $34.55   9.228%   $37.7383   $37.74   $37.75   $37.70  
  Purchase #5 $155.91   7.232%   $167.1854   $167.19   $167.20   $167.20  
  Purchase #6 $95.83   11.233%   $106.5946   $106.59   $106.60   $106.60  
  Purchase #7 $62.73   8.376%   $67.9843   $67.98   $68.00   $68.00  
  7 purchase totals = $565.46       $608.7050   $608.70   $608.75   $608.70