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 $192.37   5.788%   $203.5044   $203.50   $203.50   $203.50  
  Purchase #2 $41.48   5.386%   $43.7141   $43.71   $43.70   $43.70  
  Purchase #3 $11.68   4.630%   $12.2208   $12.22   $12.20   $12.20  
  Purchase #4 $166.27   12.394%   $186.8775   $186.88   $186.90   $186.90  
  Purchase #5 $235.45   12.353%   $264.5351   $264.54   $264.55   $264.50  
  Purchase #6 $192.60   3.799%   $199.9169   $199.92   $199.90   $199.90  
  Purchase #7 $112.83   13.416%   $127.9673   $127.97   $127.95   $128.00  
  7 purchase totals = $952.68       $1,038.7361   $1,038.74   $1,038.70   $1,038.70