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 $125.52   12.368%   $141.0443   $141.04   $141.05   $141.00  
  Purchase #2 $98.27   3.649%   $101.8559   $101.86   $101.85   $101.90  
  Purchase #3 $167.52   4.487%   $175.0366   $175.04   $175.05   $175.00  
  Purchase #4 $126.49   6.784%   $135.0711   $135.07   $135.05   $135.10  
  Purchase #5 $244.99   9.247%   $267.6442   $267.64   $267.65   $267.60  
  Purchase #6 $103.54   7.757%   $111.5716   $111.57   $111.55   $111.60  
  Purchase #7 $139.84   3.866%   $145.2462   $145.25   $145.25   $145.20  
  7 purchase totals = $1,006.17       $1,077.4699   $1,077.47   $1,077.45   $1,077.40