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 $88.66   11.176%   $98.5686   $98.57   $98.55   $98.60  
  Purchase #2 $107.85   7.402%   $115.8331   $115.83   $115.85   $115.80  
  Purchase #3 $172.74   6.332%   $183.6779   $183.68   $183.70   $183.70  
  Purchase #4 $146.97   13.144%   $166.2877   $166.29   $166.30   $166.30  
  Purchase #5 $92.78   11.871%   $103.7939   $103.79   $103.80   $103.80  
  Purchase #6 $197.57   12.193%   $221.6597   $221.66   $221.65   $221.70  
  Purchase #7 $179.72   8.776%   $195.4922   $195.49   $195.50   $195.50  
  7 purchase totals = $986.29       $1,085.3131   $1,085.31   $1,085.35   $1,085.40