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   4.397%   $43.8363   $43.84   $43.85   $43.80  
  Purchase #2 $153.80   13.257%   $174.1893   $174.19   $174.20   $174.20  
  Purchase #3 $199.40   4.653%   $208.6781   $208.68   $208.70   $208.70  
  Purchase #4 $213.99   5.756%   $226.3073   $226.31   $226.30   $226.30  
  Purchase #5 $139.65   3.816%   $144.979   $144.98   $145.00   $145.00  
  Purchase #6 $199.41   9.484%   $218.322   $218.32   $218.30   $218.30  
  Purchase #7 $203.99   9.162%   $222.6796   $222.68   $222.70   $222.70  
  7 purchase totals = $1,152.23       $1,238.9916   $1,239.00   $1,239.05   $1,239.00