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 $55.96   5.552%   $59.0669   $59.07   $59.05   $59.10  
  Purchase #2 $240.81   11.462%   $268.4116   $268.41   $268.40   $268.40  
  Purchase #3 $51.32   3.128%   $52.9253   $52.93   $52.95   $52.90  
  Purchase #4 $207.77   7.667%   $223.6997   $223.70   $223.70   $223.70  
  Purchase #5 $187.67   7.452%   $201.6552   $201.66   $201.65   $201.70  
  Purchase #6 $103.63   6.714%   $110.5877   $110.59   $110.60   $110.60  
  Purchase #7 $26.54   13.133%   $30.0255   $30.03   $30.05   $30.00  
  7 purchase totals = $873.70       $946.3719   $946.39   $946.40   $946.40