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 $85.92   7.717%   $92.5504   $92.55   $92.55   $92.60  
  Purchase #2 $85.40   7.665%   $91.9459   $91.95   $91.95   $91.90  
  Purchase #3 $236.63   13.826%   $269.3465   $269.35   $269.35   $269.30  
  Purchase #4 $80.49   4.529%   $84.1354   $84.14   $84.15   $84.10  
  Purchase #5 $123.41   10.678%   $136.5877   $136.59   $136.60   $136.60  
  Purchase #6 $136.57   8.133%   $147.6772   $147.68   $147.70   $147.70  
  Purchase #7 $191.50   5.371%   $201.7855   $201.79   $201.80   $201.80  
  7 purchase totals = $939.92       $1,024.0286   $1,024.05   $1,024.10   $1,024.00