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 $23.93   10.225%   $26.3768   $26.38   $26.40   $26.40  
  Purchase #2 $157.38   10.471%   $173.8593   $173.86   $173.85   $173.90  
  Purchase #3 $9.25   6.372%   $9.8394   $9.84   $9.85   $9.80  
  Purchase #4 $123.33   12.451%   $138.6858   $138.69   $138.70   $138.70  
  Purchase #5 $231.90   6.445%   $246.846   $246.85   $246.85   $246.80  
  Purchase #6 $105.58   4.685%   $110.5264   $110.53   $110.55   $110.50  
  Purchase #7 $43.94   9.844%   $48.2655   $48.27   $48.25   $48.30  
  7 purchase totals = $695.31       $754.3992   $754.42   $754.45   $754.40