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 $23.79   9.193%   $25.977   $25.98   $26.00   $26.00  
  Purchase #2 $71.61   5.685%   $75.681   $75.68   $75.70   $75.70  
  Purchase #3 $127.68   11.424%   $142.2662   $142.27   $142.25   $142.30  
  Purchase #4 $58.65   9.156%   $64.02   $64.02   $64.00   $64.00  
  Purchase #5 $156.52   12.526%   $176.1257   $176.13   $176.15   $176.10  
  Purchase #6 $213.39   11.845%   $238.666   $238.67   $238.65   $238.70  
  Purchase #7 $186.59   7.611%   $200.7914   $200.79   $200.80   $200.80  
  7 purchase totals = $838.23       $923.5273   $923.54   $923.55   $923.60