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 $72.53   5.819%   $76.7505   $76.75   $76.75   $76.80  
  Purchase #2 $118.48   7.858%   $127.7902   $127.79   $127.80   $127.80  
  Purchase #3 $78.36   13.306%   $88.7866   $88.79   $88.80   $88.80  
  Purchase #4 $249.41   9.701%   $273.6053   $273.61   $273.60   $273.60  
  Purchase #5 $124.68   12.823%   $140.6677   $140.67   $140.65   $140.70  
  Purchase #6 $146.95   8.594%   $159.5789   $159.58   $159.60   $159.60  
  Purchase #7 $148.53   5.398%   $156.5476   $156.55   $156.55   $156.50  
  7 purchase totals = $938.94       $1,023.7268   $1,023.74   $1,023.75   $1,023.80