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 $248.54   7.763%   $267.8342   $267.83   $267.85   $267.80  
  Purchase #2 $101.44   11.695%   $113.3034   $113.30   $113.30   $113.30  
  Purchase #3 $167.91   3.826%   $174.3342   $174.33   $174.35   $174.30  
  Purchase #4 $103.92   11.778%   $116.1597   $116.16   $116.15   $116.20  
  Purchase #5 $16.26   3.651%   $16.8537   $16.85   $16.85   $16.90  
  Purchase #6 $29.36   7.403%   $31.5335   $31.53   $31.55   $31.50  
  Purchase #7 $231.35   12.354%   $259.931   $259.93   $259.95   $259.90  
  7 purchase totals = $898.78       $979.9497   $979.93   $980.00   $979.90