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 $67.28   4.713%   $70.4509   $70.45   $70.45   $70.50  
  Purchase #2 $32.89   3.683%   $34.1013   $34.10   $34.10   $34.10  
  Purchase #3 $143.26   3.607%   $148.4274   $148.43   $148.45   $148.40  
  Purchase #4 $249.49   6.772%   $266.3855   $266.39   $266.40   $266.40  
  Purchase #5 $241.41   13.132%   $273.112   $273.11   $273.10   $273.10  
  Purchase #6 $68.85   11.684%   $76.8944   $76.89   $76.90   $76.90  
  Purchase #7 $14.76   13.121%   $16.6967   $16.70   $16.70   $16.70  
  7 purchase totals = $817.94       $886.0682   $886.07   $886.10   $886.10