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 $62.49   9.730%   $68.5703   $68.57   $68.55   $68.60  
  Purchase #2 $14.64   11.205%   $16.2804   $16.28   $16.30   $16.30  
  Purchase #3 $30.40   13.616%   $34.5393   $34.54   $34.55   $34.50  
  Purchase #4 $109.29   5.528%   $115.3316   $115.33   $115.35   $115.30  
  Purchase #5 $244.25   11.644%   $272.6905   $272.69   $272.70   $272.70  
  Purchase #6 $211.79   10.778%   $234.6167   $234.62   $234.60   $234.60  
  Purchase #7 $249.56   3.495%   $258.2821   $258.28   $258.30   $258.30  
  7 purchase totals = $922.42       $1,000.3109   $1,000.31   $1,000.35   $1,000.30