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 $41.99   11.179%   $46.6841   $46.68   $46.70   $46.70  
  Purchase #2 $56.37   3.720%   $58.467   $58.47   $58.45   $58.50  
  Purchase #3 $120.83   13.784%   $137.4852   $137.49   $137.50   $137.50  
  Purchase #4 $223.79   4.798%   $234.5274   $234.53   $234.55   $234.50  
  Purchase #5 $69.66   13.723%   $79.2194   $79.22   $79.20   $79.20  
  Purchase #6 $162.85   7.257%   $174.668   $174.67   $174.65   $174.70  
  Purchase #7 $116.90   5.590%   $123.4347   $123.43   $123.45   $123.40  
  7 purchase totals = $792.39       $854.4858   $854.49   $854.50   $854.50