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 $58.72   11.103%   $65.2397   $65.24   $65.25   $65.20  
  Purchase #2 $92.99   4.110%   $96.8119   $96.81   $96.80   $96.80  
  Purchase #3 $124.94   9.466%   $136.7668   $136.77   $136.75   $136.80  
  Purchase #4 $35.70   9.138%   $38.9623   $38.96   $38.95   $39.00  
  Purchase #5 $205.43   4.437%   $214.5449   $214.54   $214.55   $214.50  
  Purchase #6 $220.89   3.403%   $228.4069   $228.41   $228.40   $228.40  
  Purchase #7 $69.42   7.170%   $74.3974   $74.40   $74.40   $74.40  
  7 purchase totals = $808.09       $855.1299   $855.13   $855.10   $855.10