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 $41.86   11.297%   $46.5889   $46.59   $46.60   $46.60  
  Purchase #2 $52.82   13.344%   $59.8683   $59.87   $59.85   $59.90  
  Purchase #3 $51.29   11.122%   $56.9945   $56.99   $57.00   $57.00  
  Purchase #4 $216.67   8.121%   $234.2658   $234.27   $234.25   $234.30  
  Purchase #5 $110.51   3.155%   $113.9966   $114.00   $114.00   $114.00  
  Purchase #6 $43.69   7.855%   $47.1218   $47.12   $47.10   $47.10  
  Purchase #7 $143.52   9.649%   $157.3682   $157.37   $157.35   $157.40  
  7 purchase totals = $660.36       $716.2041   $716.21   $716.15   $716.30