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 $61.60   11.477%   $68.6698   $68.67   $68.65   $68.70  
  Purchase #2 $242.92   5.204%   $255.5616   $255.56   $255.55   $255.60  
  Purchase #3 $81.85   7.873%   $88.2941   $88.29   $88.30   $88.30  
  Purchase #4 $26.76   5.579%   $28.2529   $28.25   $28.25   $28.30  
  Purchase #5 $106.75   4.486%   $111.5388   $111.54   $111.55   $111.50  
  Purchase #6 $112.98   8.266%   $122.3189   $122.32   $122.30   $122.30  
  Purchase #7 $246.51   3.274%   $254.5807   $254.58   $254.60   $254.60  
  7 purchase totals = $879.37       $929.2168   $929.21   $929.20   $929.30