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 $195.62   12.682%   $220.4285   $220.43   $220.45   $220.40  
  Purchase #2 $201.25   7.701%   $216.7483   $216.75   $216.75   $216.70  
  Purchase #3 $197.83   8.608%   $214.8592   $214.86   $214.85   $214.90  
  Purchase #4 $162.99   4.845%   $170.8869   $170.89   $170.90   $170.90  
  Purchase #5 $47.50   4.112%   $49.4532   $49.45   $49.45   $49.50  
  Purchase #6 $8.27   4.856%   $8.6716   $8.67   $8.65   $8.70  
  Purchase #7 $248.64   4.783%   $260.5325   $260.53   $260.55   $260.50  
  7 purchase totals = $1,062.10       $1,141.5802   $1,141.58   $1,141.60   $1,141.60