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 $243.49   9.235%   $265.9763   $265.98   $266.00   $266.00  
  Purchase #2 $56.38   13.662%   $64.0826   $64.08   $64.10   $64.10  
  Purchase #3 $248.36   11.115%   $275.9652   $275.97   $275.95   $276.00  
  Purchase #4 $50.51   6.115%   $53.5987   $53.60   $53.60   $53.60  
  Purchase #5 $16.78   12.685%   $18.9085   $18.91   $18.90   $18.90  
  Purchase #6 $141.41   11.815%   $158.1176   $158.12   $158.10   $158.10  
  Purchase #7 $230.65   5.466%   $243.2573   $243.26   $243.25   $243.30  
  7 purchase totals = $987.58       $1,079.9062   $1,079.92   $1,079.90   $1,080.00