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 $69.91   4.255%   $72.8847   $72.88   $72.90   $72.90  
  Purchase #2 $240.50   9.655%   $263.7203   $263.72   $263.70   $263.70  
  Purchase #3 $12.66   7.126%   $13.5622   $13.56   $13.55   $13.60  
  Purchase #4 $234.32   5.400%   $246.9733   $246.97   $246.95   $247.00  
  Purchase #5 $184.53   4.825%   $193.4336   $193.43   $193.45   $193.40  
  Purchase #6 $71.80   9.558%   $78.6626   $78.66   $78.65   $78.70  
  Purchase #7 $215.44   5.149%   $226.533   $226.53   $226.55   $226.50  
  7 purchase totals = $1,029.16       $1,095.7697   $1,095.75   $1,095.75   $1,095.80