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 $50.46   6.186%   $53.5815   $53.58   $53.60   $53.60  
  Purchase #2 $163.40   12.318%   $183.5276   $183.53   $183.55   $183.50  
  Purchase #3 $187.52   5.318%   $197.4923   $197.49   $197.50   $197.50  
  Purchase #4 $91.70   12.278%   $102.9589   $102.96   $102.95   $103.00  
  Purchase #5 $238.39   10.197%   $262.6986   $262.70   $262.70   $262.70  
  Purchase #6 $133.97   8.627%   $145.5276   $145.53   $145.55   $145.50  
  Purchase #7 $51.87   9.120%   $56.6005   $56.60   $56.60   $56.60  
  7 purchase totals = $917.31       $1,002.3870   $1,002.39   $1,002.45   $1,002.40