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 $185.72   3.123%   $191.52   $191.52   $191.50   $191.50  
  Purchase #2 $51.44   8.204%   $55.6601   $55.66   $55.65   $55.70  
  Purchase #3 $12.55   12.444%   $14.1117   $14.11   $14.10   $14.10  
  Purchase #4 $157.29   3.526%   $162.836   $162.84   $162.85   $162.80  
  Purchase #5 $158.38   10.628%   $175.2126   $175.21   $175.20   $175.20  
  Purchase #6 $197.86   4.196%   $206.1622   $206.16   $206.15   $206.20  
  Purchase #7 $228.96   12.144%   $256.7649   $256.76   $256.75   $256.80  
  7 purchase totals = $992.20       $1,062.2675   $1,062.26   $1,062.20   $1,062.30