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 $56.85   10.537%   $62.8403   $62.84   $62.85   $62.80  
  Purchase #2 $245.97   10.375%   $271.4894   $271.49   $271.50   $271.50  
  Purchase #3 $219.73   4.569%   $229.7695   $229.77   $229.75   $229.80  
  Purchase #4 $62.25   8.552%   $67.5736   $67.57   $67.55   $67.60  
  Purchase #5 $46.32   10.119%   $51.0071   $51.01   $51.00   $51.00  
  Purchase #6 $240.79   10.706%   $266.569   $266.57   $266.55   $266.60  
  Purchase #7 $204.37   3.202%   $210.9139   $210.91   $210.90   $210.90  
  7 purchase totals = $1,076.28       $1,160.1628   $1,160.16   $1,160.10   $1,160.20