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 $56.44   10.155%   $62.1715   $62.17   $62.15   $62.20  
  Purchase #2 $244.77   9.644%   $268.3756   $268.38   $268.40   $268.40  
  Purchase #3 $12.88   11.498%   $14.3609   $14.36   $14.35   $14.40  
  Purchase #4 $250.68   13.487%   $284.4892   $284.49   $284.50   $284.50  
  Purchase #5 $188.62   3.336%   $194.9124   $194.91   $194.90   $194.90  
  Purchase #6 $107.30   8.112%   $116.0042   $116.00   $116.00   $116.00  
  Purchase #7 $52.65   13.685%   $59.8552   $59.86   $59.85   $59.90  
  7 purchase totals = $913.34       $1,000.1690   $1,000.17   $1,000.15   $1,000.30