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 $116.79   8.381%   $126.5782   $126.58   $126.60   $126.60  
  Purchase #2 $167.94   9.498%   $183.8909   $183.89   $183.90   $183.90  
  Purchase #3 $191.50   13.614%   $217.5708   $217.57   $217.55   $217.60  
  Purchase #4 $202.34   5.318%   $213.1004   $213.10   $213.10   $213.10  
  Purchase #5 $36.62   5.699%   $38.707   $38.71   $38.70   $38.70  
  Purchase #6 $129.44   4.798%   $135.6505   $135.65   $135.65   $135.70  
  Purchase #7 $144.25   3.792%   $149.72   $149.72   $149.70   $149.70  
  7 purchase totals = $988.88       $1,065.2178   $1,065.22   $1,065.20   $1,065.30