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 $62.32   10.651%   $68.9577   $68.96   $68.95   $69.00  
  Purchase #2 $36.70   8.779%   $39.9219   $39.92   $39.90   $39.90  
  Purchase #3 $225.64   11.295%   $251.126   $251.13   $251.15   $251.10  
  Purchase #4 $188.54   3.179%   $194.5337   $194.53   $194.55   $194.50  
  Purchase #5 $22.25   9.249%   $24.3079   $24.31   $24.30   $24.30  
  Purchase #6 $233.66   9.597%   $256.0844   $256.08   $256.10   $256.10  
  Purchase #7 $168.96   13.659%   $192.0382   $192.04   $192.05   $192.00  
  7 purchase totals = $938.07       $1,026.9698   $1,026.97   $1,027.00   $1,026.90