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 $61.87   8.185%   $66.9341   $66.93   $66.95   $66.90  
  Purchase #2 $8.72   7.800%   $9.4002   $9.40   $9.40   $9.40  
  Purchase #3 $177.37   8.400%   $192.2691   $192.27   $192.25   $192.30  
  Purchase #4 $72.77   13.333%   $82.4724   $82.47   $82.45   $82.50  
  Purchase #5 $200.46   9.675%   $219.8545   $219.85   $219.85   $219.90  
  Purchase #6 $209.99   7.456%   $225.6469   $225.65   $225.65   $225.60  
  Purchase #7 $218.53   13.679%   $248.4227   $248.42   $248.40   $248.40  
  7 purchase totals = $949.71       $1,044.9999   $1,044.99   $1,044.95   $1,045.00