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 $145.90   10.683%   $161.4865   $161.49   $161.50   $161.50  
  Purchase #2 $206.79   6.491%   $220.2127   $220.21   $220.20   $220.20  
  Purchase #3 $15.44   13.302%   $17.4938   $17.49   $17.50   $17.50  
  Purchase #4 $44.88   13.138%   $50.7763   $50.78   $50.80   $50.80  
  Purchase #5 $203.62   11.303%   $226.6352   $226.64   $226.65   $226.60  
  Purchase #6 $147.75   5.871%   $156.4244   $156.42   $156.40   $156.40  
  Purchase #7 $128.89   10.149%   $141.971   $141.97   $141.95   $142.00  
  7 purchase totals = $893.27       $974.9999   $975.00   $975.00   $975.00