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 $193.40   8.454%   $209.75   $209.75   $209.75   $209.80  
  Purchase #2 $221.83   6.226%   $235.6411   $235.64   $235.65   $235.60  
  Purchase #3 $50.65   6.793%   $54.0907   $54.09   $54.10   $54.10  
  Purchase #4 $211.30   10.872%   $234.2725   $234.27   $234.25   $234.30  
  Purchase #5 $178.94   4.202%   $186.4591   $186.46   $186.45   $186.50  
  Purchase #6 $68.89   9.822%   $75.6564   $75.66   $75.65   $75.70  
  Purchase #7 $197.84   4.292%   $206.3313   $206.33   $206.35   $206.30  
  7 purchase totals = $1,122.85       $1,202.2011   $1,202.20   $1,202.20   $1,202.30