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 $61.82   10.645%   $68.4007   $68.40   $68.40   $68.40  
  Purchase #2 $226.72   12.307%   $254.6224   $254.62   $254.60   $254.60  
  Purchase #3 $11.57   3.147%   $11.9341   $11.93   $11.95   $11.90  
  Purchase #4 $173.28   9.588%   $189.8941   $189.89   $189.90   $189.90  
  Purchase #5 $179.71   4.240%   $187.3297   $187.33   $187.35   $187.30  
  Purchase #6 $122.80   8.421%   $133.141   $133.14   $133.15   $133.10  
  Purchase #7 $109.59   3.514%   $113.441   $113.44   $113.45   $113.40  
  7 purchase totals = $885.49       $958.7630   $958.75   $958.80   $958.60