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 $59.52   9.269%   $65.0369   $65.04   $65.05   $65.00  
  Purchase #2 $91.97   11.377%   $102.4334   $102.43   $102.45   $102.40  
  Purchase #3 $221.40   8.309%   $239.7961   $239.80   $239.80   $239.80  
  Purchase #4 $56.80   5.347%   $59.8371   $59.84   $59.85   $59.80  
  Purchase #5 $11.94   3.302%   $12.3343   $12.33   $12.35   $12.30  
  Purchase #6 $109.51   4.855%   $114.8267   $114.83   $114.85   $114.80  
  Purchase #7 $223.89   12.583%   $252.0621   $252.06   $252.05   $252.10  
  7 purchase totals = $775.03       $846.3266   $846.33   $846.40   $846.20