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 $91.37   4.269%   $95.2706   $95.27   $95.25   $95.30  
  Purchase #2 $29.99   8.737%   $32.6102   $32.61   $32.60   $32.60  
  Purchase #3 $147.79   12.213%   $165.8396   $165.84   $165.85   $165.80  
  Purchase #4 $183.82   5.218%   $193.4117   $193.41   $193.40   $193.40  
  Purchase #5 $174.42   9.432%   $190.8713   $190.87   $190.85   $190.90  
  Purchase #6 $223.74   13.537%   $254.0277   $254.03   $254.05   $254.00  
  Purchase #7 $23.30   8.306%   $25.2353   $25.24   $25.25   $25.20  
  7 purchase totals = $874.43       $957.2664   $957.27   $957.25   $957.20