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 $235.57   11.354%   $262.3166   $262.32   $262.30   $262.30  
  Purchase #2 $248.98   9.536%   $272.7227   $272.72   $272.70   $272.70  
  Purchase #3 $141.82   5.612%   $149.7789   $149.78   $149.80   $149.80  
  Purchase #4 $66.42   5.248%   $69.9057   $69.91   $69.90   $69.90  
  Purchase #5 $71.58   6.660%   $76.3472   $76.35   $76.35   $76.30  
  Purchase #6 $71.77   12.389%   $80.6616   $80.66   $80.65   $80.70  
  Purchase #7 $97.66   9.417%   $106.8566   $106.86   $106.85   $106.90  
  7 purchase totals = $933.80       $1,018.5893   $1,018.60   $1,018.55   $1,018.60