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 $44.83   11.555%   $50.0101   $50.01   $50.00   $50.00  
  Purchase #2 $212.88   8.343%   $230.6406   $230.64   $230.65   $230.60  
  Purchase #3 $204.81   6.255%   $217.6209   $217.62   $217.60   $217.60  
  Purchase #4 $42.45   3.264%   $43.8356   $43.84   $43.85   $43.80  
  Purchase #5 $245.43   5.615%   $259.2109   $259.21   $259.20   $259.20  
  Purchase #6 $172.72   8.297%   $187.0506   $187.05   $187.05   $187.10  
  Purchase #7 $115.34   7.456%   $123.9398   $123.94   $123.95   $123.90  
  7 purchase totals = $1,038.46       $1,112.3085   $1,112.31   $1,112.30   $1,112.20