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 $204.84   11.210%   $227.8026   $227.80   $227.80   $227.80  
  Purchase #2 $140.99   7.571%   $151.6644   $151.66   $151.65   $151.70  
  Purchase #3 $79.76   11.604%   $89.0154   $89.02   $89.00   $89.00  
  Purchase #4 $61.57   13.269%   $69.7397   $69.74   $69.75   $69.70  
  Purchase #5 $103.36   3.124%   $106.589   $106.59   $106.60   $106.60  
  Purchase #6 $76.27   7.586%   $82.0558   $82.06   $82.05   $82.10  
  Purchase #7 $121.93   4.850%   $127.8436   $127.84   $127.85   $127.80  
  7 purchase totals = $788.72       $854.7105   $854.71   $854.70   $854.70