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 $59.62   10.126%   $65.6571   $65.66   $65.65   $65.70  
  Purchase #2 $226.29   4.388%   $236.2196   $236.22   $236.20   $236.20  
  Purchase #3 $174.89   13.209%   $197.9912   $197.99   $198.00   $198.00  
  Purchase #4 $230.72   12.620%   $259.8369   $259.84   $259.85   $259.80  
  Purchase #5 $75.70   12.682%   $85.3003   $85.30   $85.30   $85.30  
  Purchase #6 $83.51   7.547%   $89.8125   $89.81   $89.80   $89.80  
  Purchase #7 $137.68   13.835%   $156.728   $156.73   $156.75   $156.70  
  7 purchase totals = $988.41       $1,091.5456   $1,091.55   $1,091.55   $1,091.50