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 $74.81   10.146%   $82.4002   $82.40   $82.40   $82.40  
  Purchase #2 $174.92   6.810%   $186.8321   $186.83   $186.85   $186.80  
  Purchase #3 $81.28   6.662%   $86.6949   $86.69   $86.70   $86.70  
  Purchase #4 $105.49   12.484%   $118.6594   $118.66   $118.65   $118.70  
  Purchase #5 $99.81   10.615%   $110.4048   $110.40   $110.40   $110.40  
  Purchase #6 $118.87   9.400%   $130.0438   $130.04   $130.05   $130.00  
  Purchase #7 $39.99   3.128%   $41.2409   $41.24   $41.25   $41.20  
  7 purchase totals = $695.17       $756.2761   $756.26   $756.30   $756.20