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 $134.54   6.488%   $143.269   $143.27   $143.25   $143.30  
  Purchase #2 $231.34   13.708%   $263.0521   $263.05   $263.05   $263.10  
  Purchase #3 $201.42   9.268%   $220.0876   $220.09   $220.10   $220.10  
  Purchase #4 $173.63   4.222%   $180.9607   $180.96   $180.95   $181.00  
  Purchase #5 $166.61   11.220%   $185.3036   $185.30   $185.30   $185.30  
  Purchase #6 $70.64   13.109%   $79.9002   $79.90   $79.90   $79.90  
  Purchase #7 $57.89   3.254%   $59.7737   $59.77   $59.75   $59.80  
  7 purchase totals = $1,036.07       $1,132.3469   $1,132.34   $1,132.30   $1,132.50