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 $74.91   6.167%   $79.5297   $79.53   $79.55   $79.50  
  Purchase #2 $122.39   3.790%   $127.0286   $127.03   $127.05   $127.00  
  Purchase #3 $191.50   8.449%   $207.6798   $207.68   $207.70   $207.70  
  Purchase #4 $99.87   6.729%   $106.5903   $106.59   $106.60   $106.60  
  Purchase #5 $102.76   13.780%   $116.9203   $116.92   $116.90   $116.90  
  Purchase #6 $83.62   13.617%   $95.0065   $95.01   $95.00   $95.00  
  Purchase #7 $69.40   3.173%   $71.6021   $71.60   $71.60   $71.60  
  7 purchase totals = $744.45       $804.3573   $804.36   $804.40   $804.30