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 $245.87   9.274%   $268.672   $268.67   $268.65   $268.70  
  Purchase #2 $120.72   13.803%   $137.383   $137.38   $137.40   $137.40  
  Purchase #3 $184.88   4.786%   $193.7284   $193.73   $193.75   $193.70  
  Purchase #4 $70.49   3.209%   $72.752   $72.75   $72.75   $72.80  
  Purchase #5 $129.57   5.184%   $136.2869   $136.29   $136.30   $136.30  
  Purchase #6 $36.34   3.287%   $37.5345   $37.53   $37.55   $37.50  
  Purchase #7 $147.78   11.867%   $165.3171   $165.32   $165.30   $165.30  
  7 purchase totals = $935.65       $1,011.6739   $1,011.67   $1,011.70   $1,011.70