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 $61.94   3.423%   $64.0602   $64.06   $64.05   $64.10  
  Purchase #2 $110.52   7.754%   $119.0897   $119.09   $119.10   $119.10  
  Purchase #3 $250.86   11.125%   $278.7682   $278.77   $278.75   $278.80  
  Purchase #4 $85.38   3.339%   $88.2308   $88.23   $88.25   $88.20  
  Purchase #5 $23.79   3.747%   $24.6814   $24.68   $24.70   $24.70  
  Purchase #6 $224.68   3.600%   $232.7685   $232.77   $232.75   $232.80  
  Purchase #7 $7.25   5.329%   $7.6364   $7.64   $7.65   $7.60  
  7 purchase totals = $764.42       $815.2352   $815.24   $815.25   $815.30