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 $202.88   10.841%   $224.8742   $224.87   $224.85   $224.90  
  Purchase #2 $230.72   7.594%   $248.2409   $248.24   $248.25   $248.20  
  Purchase #3 $171.55   7.197%   $183.8965   $183.90   $183.90   $183.90  
  Purchase #4 $246.48   7.594%   $265.1977   $265.20   $265.20   $265.20  
  Purchase #5 $110.58   8.173%   $119.6177   $119.62   $119.60   $119.60  
  Purchase #6 $22.46   8.353%   $24.3361   $24.34   $24.35   $24.30  
  Purchase #7 $62.54   5.808%   $66.1723   $66.17   $66.15   $66.20  
  7 purchase totals = $1,047.21       $1,132.3354   $1,132.34   $1,132.30   $1,132.30