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 $103.56   10.701%   $114.642   $114.64   $114.65   $114.60  
  Purchase #2 $57.40   4.544%   $60.0083   $60.01   $60.00   $60.00  
  Purchase #3 $219.67   6.525%   $234.0035   $234.00   $234.00   $234.00  
  Purchase #4 $69.54   5.295%   $73.2221   $73.22   $73.20   $73.20  
  Purchase #5 $81.65   4.818%   $85.5839   $85.58   $85.60   $85.60  
  Purchase #6 $103.50   7.405%   $111.1642   $111.16   $111.15   $111.20  
  Purchase #7 $234.81   4.870%   $246.2452   $246.25   $246.25   $246.20  
  7 purchase totals = $870.13       $924.8692   $924.86   $924.85   $924.80