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 $229.39   7.867%   $247.4361   $247.44   $247.45   $247.40  
  Purchase #2 $44.55   3.260%   $46.0023   $46.00   $46.00   $46.00  
  Purchase #3 $49.26   11.766%   $55.0559   $55.06   $55.05   $55.10  
  Purchase #4 $64.37   3.295%   $66.491   $66.49   $66.50   $66.50  
  Purchase #5 $226.85   5.268%   $238.8005   $238.80   $238.80   $238.80  
  Purchase #6 $152.57   7.493%   $164.0021   $164.00   $164.00   $164.00  
  Purchase #7 $178.88   10.679%   $197.9826   $197.98   $198.00   $198.00  
  7 purchase totals = $945.87       $1,015.7705   $1,015.77   $1,015.80   $1,015.80