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 $54.43   9.487%   $59.5938   $59.59   $59.60   $59.60  
  Purchase #2 $232.61   3.147%   $239.9302   $239.93   $239.95   $239.90  
  Purchase #3 $39.87   5.166%   $41.9297   $41.93   $41.95   $41.90  
  Purchase #4 $106.97   13.523%   $121.4356   $121.44   $121.45   $121.40  
  Purchase #5 $33.75   7.213%   $36.1844   $36.18   $36.20   $36.20  
  Purchase #6 $200.37   8.827%   $218.0567   $218.06   $218.05   $218.10  
  Purchase #7 $38.66   9.550%   $42.352   $42.35   $42.35   $42.40  
  7 purchase totals = $706.66       $759.4824   $759.48   $759.55   $759.50