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   8.395%   $61.5684   $61.57   $61.55   $61.60  
  Purchase #2 $148.93   8.264%   $161.2376   $161.24   $161.25   $161.20  
  Purchase #3 $41.93   12.381%   $47.1214   $47.12   $47.10   $47.10  
  Purchase #4 $75.95   4.199%   $79.1391   $79.14   $79.15   $79.10  
  Purchase #5 $100.36   13.551%   $113.9598   $113.96   $113.95   $114.00  
  Purchase #6 $26.41   4.142%   $27.5039   $27.50   $27.50   $27.50  
  Purchase #7 $225.38   9.527%   $246.852   $246.85   $246.85   $246.90  
  7 purchase totals = $675.76       $737.3822   $737.38   $737.35   $737.40