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 $178.87   13.837%   $203.6202   $203.62   $203.60   $203.60  
  Purchase #2 $79.47   12.832%   $89.6676   $89.67   $89.65   $89.70  
  Purchase #3 $32.39   10.187%   $35.6896   $35.69   $35.70   $35.70  
  Purchase #4 $5.59   5.808%   $5.9147   $5.91   $5.90   $5.90  
  Purchase #5 $118.40   5.238%   $124.6018   $124.60   $124.60   $124.60  
  Purchase #6 $235.91   4.743%   $247.0992   $247.10   $247.10   $247.10  
  Purchase #7 $182.90   10.413%   $201.9454   $201.95   $201.95   $201.90  
  7 purchase totals = $833.53       $908.5385   $908.54   $908.50   $908.50