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 $56.80   8.423%   $61.5843   $61.58   $61.60   $61.60  
  Purchase #2 $110.44   13.392%   $125.2301   $125.23   $125.25   $125.20  
  Purchase #3 $106.77   10.530%   $118.0129   $118.01   $118.00   $118.00  
  Purchase #4 $38.59   6.713%   $41.1805   $41.18   $41.20   $41.20  
  Purchase #5 $79.37   7.581%   $85.387   $85.39   $85.40   $85.40  
  Purchase #6 $211.97   9.398%   $231.8909   $231.89   $231.90   $231.90  
  Purchase #7 $19.73   11.273%   $21.9542   $21.95   $21.95   $22.00  
  7 purchase totals = $623.67       $685.2399   $685.23   $685.30   $685.30