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 $69.85   8.846%   $76.0289   $76.03   $76.05   $76.00  
  Purchase #2 $58.96   6.396%   $62.7311   $62.73   $62.75   $62.70  
  Purchase #3 $114.88   5.648%   $121.3684   $121.37   $121.35   $121.40  
  Purchase #4 $121.37   10.716%   $134.376   $134.38   $134.40   $134.40  
  Purchase #5 $189.84   4.599%   $198.5707   $198.57   $198.55   $198.60  
  Purchase #6 $76.87   4.261%   $80.1454   $80.15   $80.15   $80.10  
  Purchase #7 $184.88   10.318%   $203.9559   $203.96   $203.95   $204.00  
  7 purchase totals = $816.65       $877.1764   $877.19   $877.20   $877.20