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 $26.58   11.432%   $29.6186   $29.62   $29.60   $29.60  
  Purchase #2 $88.86   7.475%   $95.5023   $95.50   $95.50   $95.50  
  Purchase #3 $222.98   8.490%   $241.911   $241.91   $241.90   $241.90  
  Purchase #4 $10.92   7.170%   $11.703   $11.70   $11.70   $11.70  
  Purchase #5 $168.34   4.598%   $176.0803   $176.08   $176.10   $176.10  
  Purchase #6 $194.67   7.268%   $208.8186   $208.82   $208.80   $208.80  
  Purchase #7 $211.49   12.392%   $237.6978   $237.70   $237.70   $237.70  
  7 purchase totals = $923.84       $1,001.3316   $1,001.33   $1,001.30   $1,001.30