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 $61.72   7.311%   $66.2323   $66.23   $66.25   $66.20  
  Purchase #2 $237.85   9.102%   $259.4991   $259.50   $259.50   $259.50  
  Purchase #3 $27.76   3.278%   $28.67   $28.67   $28.65   $28.70  
  Purchase #4 $244.96   8.581%   $265.98   $265.98   $266.00   $266.00  
  Purchase #5 $127.99   11.106%   $142.2046   $142.20   $142.20   $142.20  
  Purchase #6 $220.69   11.166%   $245.3322   $245.33   $245.35   $245.30  
  Purchase #7 $20.50   3.304%   $21.1773   $21.18   $21.20   $21.20  
  7 purchase totals = $941.47       $1,029.0955   $1,029.09   $1,029.15   $1,029.10