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 $189.96   8.436%   $205.985   $205.99   $206.00   $206.00  
  Purchase #2 $167.48   8.647%   $181.962   $181.96   $181.95   $182.00  
  Purchase #3 $87.99   8.410%   $95.39   $95.39   $95.40   $95.40  
  Purchase #4 $168.68   3.626%   $174.7963   $174.80   $174.80   $174.80  
  Purchase #5 $111.83   10.275%   $123.3205   $123.32   $123.30   $123.30  
  Purchase #6 $75.90   3.367%   $78.4556   $78.46   $78.45   $78.50  
  Purchase #7 $22.88   4.693%   $23.9538   $23.95   $23.95   $24.00  
  7 purchase totals = $824.72       $883.8632   $883.87   $883.85   $884.00