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 $100.28   3.481%   $103.7707   $103.77   $103.75   $103.80  
  Purchase #2 $53.45   10.399%   $59.0083   $59.01   $59.00   $59.00  
  Purchase #3 $202.53   5.779%   $214.2342   $214.23   $214.25   $214.20  
  Purchase #4 $193.36   5.694%   $204.3699   $204.37   $204.35   $204.40  
  Purchase #5 $237.50   6.177%   $252.1704   $252.17   $252.15   $252.20  
  Purchase #6 $75.37   13.378%   $85.453   $85.45   $85.45   $85.50  
  Purchase #7 $92.52   13.274%   $104.8011   $104.80   $104.80   $104.80  
  7 purchase totals = $955.01       $1,023.8076   $1,023.80   $1,023.75   $1,023.90