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 $104.75   10.748%   $116.0085   $116.01   $116.00   $116.00  
  Purchase #2 $173.33   5.727%   $183.2566   $183.26   $183.25   $183.30  
  Purchase #3 $51.48   8.160%   $55.6808   $55.68   $55.70   $55.70  
  Purchase #4 $30.81   11.724%   $34.4222   $34.42   $34.40   $34.40  
  Purchase #5 $90.32   6.806%   $96.4672   $96.47   $96.45   $96.50  
  Purchase #6 $212.99   4.804%   $223.222   $223.22   $223.20   $223.20  
  Purchase #7 $84.99   8.586%   $92.2872   $92.29   $92.30   $92.30  
  7 purchase totals = $748.67       $801.3445   $801.35   $801.30   $801.40