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 $85.82   12.565%   $96.6033   $96.60   $96.60   $96.60  
  Purchase #2 $131.97   8.144%   $142.7176   $142.72   $142.70   $142.70  
  Purchase #3 $245.26   9.346%   $268.182   $268.18   $268.20   $268.20  
  Purchase #4 $208.92   3.254%   $215.7183   $215.72   $215.70   $215.70  
  Purchase #5 $29.71   10.637%   $32.8703   $32.87   $32.85   $32.90  
  Purchase #6 $103.52   7.126%   $110.8968   $110.90   $110.90   $110.90  
  Purchase #7 $137.55   5.169%   $144.66   $144.66   $144.65   $144.70  
  7 purchase totals = $942.75       $1,011.6483   $1,011.65   $1,011.60   $1,011.70