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 $20.79   6.635%   $22.1694   $22.17   $22.15   $22.20  
  Purchase #2 $38.45   13.537%   $43.655   $43.66   $43.65   $43.70  
  Purchase #3 $9.34   11.178%   $10.384   $10.38   $10.40   $10.40  
  Purchase #4 $207.48   9.181%   $226.5287   $226.53   $226.55   $226.50  
  Purchase #5 $238.84   11.188%   $265.5614   $265.56   $265.55   $265.60  
  Purchase #6 $25.45   8.612%   $27.6418   $27.64   $27.65   $27.60  
  Purchase #7 $74.45   3.395%   $76.9776   $76.98   $77.00   $77.00  
  7 purchase totals = $614.80       $672.9179   $672.92   $672.95   $673.00