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 $84.77   12.333%   $95.2247   $95.22   $95.20   $95.20  
  Purchase #2 $49.96   13.817%   $56.863   $56.86   $56.85   $56.90  
  Purchase #3 $220.30   12.845%   $248.5975   $248.60   $248.60   $248.60  
  Purchase #4 $172.84   9.646%   $189.5121   $189.51   $189.50   $189.50  
  Purchase #5 $53.53   12.694%   $60.3251   $60.33   $60.35   $60.30  
  Purchase #6 $226.72   8.107%   $245.1002   $245.10   $245.10   $245.10  
  Purchase #7 $110.35   3.692%   $114.4241   $114.42   $114.40   $114.40  
  7 purchase totals = $918.47       $1,010.0467   $1,010.04   $1,010.00   $1,010.00