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 $96.45   8.538%   $104.6849   $104.68   $104.70   $104.70  
  Purchase #2 $142.59   4.469%   $148.9623   $148.96   $148.95   $149.00  
  Purchase #3 $63.53   4.839%   $66.6042   $66.60   $66.60   $66.60  
  Purchase #4 $202.39   8.803%   $220.2064   $220.21   $220.20   $220.20  
  Purchase #5 $86.81   10.616%   $96.0257   $96.03   $96.05   $96.00  
  Purchase #6 $112.78   9.436%   $123.4219   $123.42   $123.40   $123.40  
  Purchase #7 $162.25   3.868%   $168.5258   $168.53   $168.55   $168.50  
  7 purchase totals = $866.80       $928.4312   $928.43   $928.45   $928.40