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 $119.55   13.623%   $135.8363   $135.84   $135.85   $135.80  
  Purchase #2 $128.67   10.246%   $141.8535   $141.85   $141.85   $141.90  
  Purchase #3 $67.95   11.554%   $75.8009   $75.80   $75.80   $75.80  
  Purchase #4 $34.58   13.550%   $39.2656   $39.27   $39.25   $39.30  
  Purchase #5 $206.30   13.671%   $234.5033   $234.50   $234.50   $234.50  
  Purchase #6 $201.78   7.220%   $216.3485   $216.35   $216.35   $216.30  
  Purchase #7 $104.98   9.786%   $115.2533   $115.25   $115.25   $115.30  
  7 purchase totals = $863.81       $958.8614   $958.86   $958.85   $958.90