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 $84.58   9.103%   $92.2793   $92.28   $92.30   $92.30  
  Purchase #2 $216.68   7.495%   $232.9202   $232.92   $232.90   $232.90  
  Purchase #3 $66.62   8.470%   $72.2627   $72.26   $72.25   $72.30  
  Purchase #4 $247.61   13.320%   $280.5917   $280.59   $280.60   $280.60  
  Purchase #5 $31.79   10.326%   $35.0726   $35.07   $35.05   $35.10  
  Purchase #6 $147.99   4.131%   $154.1035   $154.10   $154.10   $154.10  
  Purchase #7 $127.69   12.292%   $143.3857   $143.39   $143.40   $143.40  
  7 purchase totals = $922.96       $1,010.6157   $1,010.61   $1,010.60   $1,010.70