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 $95.61   10.815%   $105.9502   $105.95   $105.95   $106.00  
  Purchase #2 $45.64   4.237%   $47.5738   $47.57   $47.55   $47.60  
  Purchase #3 $53.86   10.706%   $59.6263   $59.63   $59.65   $59.60  
  Purchase #4 $238.65   6.147%   $253.3198   $253.32   $253.30   $253.30  
  Purchase #5 $23.92   9.214%   $26.124   $26.12   $26.10   $26.10  
  Purchase #6 $112.27   8.831%   $122.1846   $122.18   $122.20   $122.20  
  Purchase #7 $54.36   10.381%   $60.0031   $60.00   $60.00   $60.00  
  7 purchase totals = $624.31       $674.7818   $674.77   $674.75   $674.80