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 $57.41   4.197%   $59.8195   $59.82   $59.80   $59.80  
  Purchase #2 $168.49   4.549%   $176.1546   $176.15   $176.15   $176.20  
  Purchase #3 $16.70   8.413%   $18.105   $18.11   $18.10   $18.10  
  Purchase #4 $109.28   12.601%   $123.0504   $123.05   $123.05   $123.10  
  Purchase #5 $207.65   5.158%   $218.3606   $218.36   $218.35   $218.40  
  Purchase #6 $213.30   10.412%   $235.5088   $235.51   $235.50   $235.50  
  Purchase #7 $186.69   7.843%   $201.3321   $201.33   $201.35   $201.30  
  7 purchase totals = $959.52       $1,032.3310   $1,032.33   $1,032.30   $1,032.40