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 $86.25   7.744%   $92.9292   $92.93   $92.95   $92.90  
  Purchase #2 $167.97   7.570%   $180.6853   $180.69   $180.70   $180.70  
  Purchase #3 $43.37   9.774%   $47.609   $47.61   $47.60   $47.60  
  Purchase #4 $232.70   7.735%   $250.6993   $250.70   $250.70   $250.70  
  Purchase #5 $134.82   5.811%   $142.6544   $142.65   $142.65   $142.70  
  Purchase #6 $148.28   9.715%   $162.6854   $162.69   $162.70   $162.70  
  Purchase #7 $137.36   11.460%   $153.1015   $153.10   $153.10   $153.10  
  7 purchase totals = $950.75       $1,030.3641   $1,030.37   $1,030.40   $1,030.40