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 $23.39   11.721%   $26.1315   $26.13   $26.15   $26.10  
  Purchase #2 $216.97   5.670%   $229.2722   $229.27   $229.25   $229.30  
  Purchase #3 $16.64   5.301%   $17.5221   $17.52   $17.50   $17.50  
  Purchase #4 $163.95   7.754%   $176.6627   $176.66   $176.65   $176.70  
  Purchase #5 $163.79   11.378%   $182.426   $182.43   $182.45   $182.40  
  Purchase #6 $58.55   7.635%   $63.0203   $63.02   $63.00   $63.00  
  Purchase #7 $206.36   12.226%   $231.5896   $231.59   $231.60   $231.60  
  7 purchase totals = $849.65       $926.6244   $926.62   $926.60   $926.60