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 $106.74   12.303%   $119.8722   $119.87   $119.85   $119.90  
  Purchase #2 $236.35   11.137%   $262.6723   $262.67   $262.65   $262.70  
  Purchase #3 $9.65   10.224%   $10.6366   $10.64   $10.65   $10.60  
  Purchase #4 $15.74   13.801%   $17.9123   $17.91   $17.90   $17.90  
  Purchase #5 $165.72   5.535%   $174.8926   $174.89   $174.90   $174.90  
  Purchase #6 $92.88   12.336%   $104.3377   $104.34   $104.35   $104.30  
  Purchase #7 $229.85   7.662%   $247.4611   $247.46   $247.45   $247.50  
  7 purchase totals = $856.93       $937.7848   $937.78   $937.75   $937.80