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 $69.29   9.666%   $75.9876   $75.99   $76.00   $76.00  
  Purchase #2 $218.59   8.115%   $236.3286   $236.33   $236.35   $236.30  
  Purchase #3 $200.72   12.804%   $226.4202   $226.42   $226.40   $226.40  
  Purchase #4 $243.79   12.384%   $273.981   $273.98   $274.00   $274.00  
  Purchase #5 $174.65   4.742%   $182.9319   $182.93   $182.95   $182.90  
  Purchase #6 $202.54   5.247%   $213.1673   $213.17   $213.15   $213.20  
  Purchase #7 $55.47   11.553%   $61.8784   $61.88   $61.90   $61.90  
  7 purchase totals = $1,165.05       $1,270.6950   $1,270.70   $1,270.75   $1,270.70