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 $243.26   8.397%   $263.6865   $263.69   $263.70   $263.70  
  Purchase #2 $91.77   4.123%   $95.5537   $95.55   $95.55   $95.60  
  Purchase #3 $214.94   8.384%   $232.9606   $232.96   $232.95   $233.00  
  Purchase #4 $45.91   8.466%   $49.7967   $49.80   $49.80   $49.80  
  Purchase #5 $77.54   8.257%   $83.9425   $83.94   $83.95   $83.90  
  Purchase #6 $232.83   7.254%   $249.7195   $249.72   $249.70   $249.70  
  Purchase #7 $76.81   10.871%   $85.16   $85.16   $85.15   $85.20  
  7 purchase totals = $983.06       $1,060.8195   $1,060.82   $1,060.80   $1,060.90