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 $23.95   13.482%   $27.1789   $27.18   $27.20   $27.20  
  Purchase #2 $250.59   11.157%   $278.5483   $278.55   $278.55   $278.50  
  Purchase #3 $45.36   4.734%   $47.5073   $47.51   $47.50   $47.50  
  Purchase #4 $150.87   7.760%   $162.5775   $162.58   $162.60   $162.60  
  Purchase #5 $217.50   3.257%   $224.584   $224.58   $224.60   $224.60  
  Purchase #6 $170.44   10.140%   $187.7226   $187.72   $187.70   $187.70  
  Purchase #7 $113.47   7.442%   $121.9144   $121.91   $121.90   $121.90  
  7 purchase totals = $972.18       $1,050.0330   $1,050.03   $1,050.05   $1,050.00