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 $75.74   8.263%   $81.9984   $82.00   $82.00   $82.00  
  Purchase #2 $151.58   3.769%   $157.2931   $157.29   $157.30   $157.30  
  Purchase #3 $191.63   7.805%   $206.5867   $206.59   $206.60   $206.60  
  Purchase #4 $94.68   13.227%   $107.2033   $107.20   $107.20   $107.20  
  Purchase #5 $103.67   4.851%   $108.699   $108.70   $108.70   $108.70  
  Purchase #6 $214.61   6.157%   $227.8235   $227.82   $227.80   $227.80  
  Purchase #7 $131.27   6.793%   $140.1872   $140.19   $140.20   $140.20  
  7 purchase totals = $963.18       $1,029.7912   $1,029.79   $1,029.80   $1,029.80