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 $49.27   6.431%   $52.4386   $52.44   $52.45   $52.40  
  Purchase #2 $65.71   11.502%   $73.268   $73.27   $73.25   $73.30  
  Purchase #3 $55.63   7.850%   $59.997   $60.00   $60.00   $60.00  
  Purchase #4 $145.33   10.423%   $160.4777   $160.48   $160.50   $160.50  
  Purchase #5 $5.94   3.628%   $6.1555   $6.16   $6.15   $6.20  
  Purchase #6 $201.37   13.675%   $228.9073   $228.91   $228.90   $228.90  
  Purchase #7 $149.51   8.219%   $161.7982   $161.80   $161.80   $161.80  
  7 purchase totals = $672.76       $743.0423   $743.06   $743.05   $743.10