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 $95.53   8.615%   $103.7599   $103.76   $103.75   $103.80  
  Purchase #2 $66.39   4.735%   $69.5336   $69.53   $69.55   $69.50  
  Purchase #3 $17.73   6.433%   $18.8706   $18.87   $18.85   $18.90  
  Purchase #4 $79.65   12.159%   $89.3346   $89.33   $89.35   $89.30  
  Purchase #5 $86.66   11.560%   $96.6779   $96.68   $96.70   $96.70  
  Purchase #6 $51.92   6.754%   $55.4267   $55.43   $55.45   $55.40  
  Purchase #7 $50.59   10.701%   $56.0036   $56.00   $56.00   $56.00  
  7 purchase totals = $448.47       $489.6069   $489.60   $489.65   $489.60