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 $241.78   9.739%   $265.327   $265.33   $265.35   $265.30  
  Purchase #2 $172.51   9.460%   $188.8294   $188.83   $188.85   $188.80  
  Purchase #3 $10.76   10.273%   $11.8654   $11.87   $11.85   $11.90  
  Purchase #4 $140.47   5.581%   $148.3096   $148.31   $148.30   $148.30  
  Purchase #5 $91.27   3.729%   $94.6735   $94.67   $94.65   $94.70  
  Purchase #6 $215.90   12.734%   $243.3927   $243.39   $243.40   $243.40  
  Purchase #7 $43.94   12.104%   $49.2585   $49.26   $49.25   $49.30  
  7 purchase totals = $916.63       $1,001.6561   $1,001.66   $1,001.65   $1,001.70