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 $58.38   11.269%   $64.9588   $64.96   $64.95   $65.00  
  Purchase #2 $86.66   8.679%   $94.1812   $94.18   $94.20   $94.20  
  Purchase #3 $97.82   9.667%   $107.2763   $107.28   $107.30   $107.30  
  Purchase #4 $101.66   6.539%   $108.3075   $108.31   $108.30   $108.30  
  Purchase #5 $162.39   12.276%   $182.325   $182.33   $182.35   $182.30  
  Purchase #6 $243.99   8.727%   $265.283   $265.28   $265.30   $265.30  
  Purchase #7 $231.37   3.291%   $238.9844   $238.98   $239.00   $239.00  
  7 purchase totals = $982.27       $1,061.3162   $1,061.32   $1,061.40   $1,061.40