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 $171.61   5.366%   $180.8186   $180.82   $180.80   $180.80  
  Purchase #2 $105.60   9.113%   $115.2233   $115.22   $115.20   $115.20  
  Purchase #3 $213.30   9.720%   $234.0328   $234.03   $234.05   $234.00  
  Purchase #4 $85.89   9.328%   $93.9018   $93.90   $93.90   $93.90  
  Purchase #5 $167.41   3.305%   $172.9429   $172.94   $172.95   $172.90  
  Purchase #6 $37.97   3.740%   $39.3901   $39.39   $39.40   $39.40  
  Purchase #7 $92.70   10.553%   $102.4826   $102.48   $102.50   $102.50  
  7 purchase totals = $874.48       $938.7921   $938.78   $938.80   $938.70