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 $48.26   4.659%   $50.5084   $50.51   $50.50   $50.50  
  Purchase #2 $214.83   6.198%   $228.1452   $228.15   $228.15   $228.10  
  Purchase #3 $222.33   6.124%   $235.9455   $235.95   $235.95   $235.90  
  Purchase #4 $77.35   4.407%   $80.7588   $80.76   $80.75   $80.80  
  Purchase #5 $234.74   13.216%   $265.7632   $265.76   $265.75   $265.80  
  Purchase #6 $131.45   4.691%   $137.6163   $137.62   $137.60   $137.60  
  Purchase #7 $58.87   12.117%   $66.0033   $66.00   $66.00   $66.00  
  7 purchase totals = $987.83       $1,064.7407   $1,064.75   $1,064.70   $1,064.70