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 $52.29   6.507%   $55.6925   $55.69   $55.70   $55.70  
  Purchase #2 $208.29   11.640%   $232.535   $232.54   $232.55   $232.50  
  Purchase #3 $87.52   11.818%   $97.8631   $97.86   $97.85   $97.90  
  Purchase #4 $133.86   11.378%   $149.0906   $149.09   $149.10   $149.10  
  Purchase #5 $60.52   4.325%   $63.1375   $63.14   $63.15   $63.10  
  Purchase #6 $244.75   11.715%   $273.4225   $273.42   $273.40   $273.40  
  Purchase #7 $171.81   6.633%   $183.2062   $183.21   $183.20   $183.20  
  7 purchase totals = $959.04       $1,054.9474   $1,054.95   $1,054.95   $1,054.90