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 $62.40   8.590%   $67.7602   $67.76   $67.75   $67.80  
  Purchase #2 $217.82   9.237%   $237.94   $237.94   $237.95   $237.90  
  Purchase #3 $87.64   10.106%   $96.4969   $96.50   $96.50   $96.50  
  Purchase #4 $227.74   6.697%   $242.9917   $242.99   $243.00   $243.00  
  Purchase #5 $89.54   3.732%   $92.8816   $92.88   $92.90   $92.90  
  Purchase #6 $186.30   9.411%   $203.8327   $203.83   $203.85   $203.80  
  Purchase #7 $92.48   12.378%   $103.9272   $103.93   $103.95   $103.90  
  7 purchase totals = $963.92       $1,045.8303   $1,045.83   $1,045.90   $1,045.80