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 $86.86   10.833%   $96.2695   $96.27   $96.25   $96.30  
  Purchase #2 $224.61   10.188%   $247.4933   $247.49   $247.50   $247.50  
  Purchase #3 $219.69   5.454%   $231.6719   $231.67   $231.65   $231.70  
  Purchase #4 $149.60   5.506%   $157.837   $157.84   $157.85   $157.80  
  Purchase #5 $104.69   12.271%   $117.5365   $117.54   $117.55   $117.50  
  Purchase #6 $190.34   4.826%   $199.5258   $199.53   $199.55   $199.50  
  Purchase #7 $7.34   11.270%   $8.1672   $8.17   $8.15   $8.20  
  7 purchase totals = $983.13       $1,058.5012   $1,058.51   $1,058.50   $1,058.50