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 $184.65   11.564%   $206.0029   $206.00   $206.00   $206.00  
  Purchase #2 $57.41   7.650%   $61.8019   $61.80   $61.80   $61.80  
  Purchase #3 $53.65   4.444%   $56.0342   $56.03   $56.05   $56.00  
  Purchase #4 $91.87   8.582%   $99.7543   $99.75   $99.75   $99.80  
  Purchase #5 $110.64   5.401%   $116.6157   $116.62   $116.60   $116.60  
  Purchase #6 $164.83   12.746%   $185.8392   $185.84   $185.85   $185.80  
  Purchase #7 $68.29   12.730%   $76.9833   $76.98   $77.00   $77.00  
  7 purchase totals = $731.34       $803.0315   $803.02   $803.05   $803.00