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 $192.71   7.181%   $206.5485   $206.55   $206.55   $206.50  
  Purchase #2 $65.47   3.282%   $67.6187   $67.62   $67.60   $67.60  
  Purchase #3 $182.49   10.103%   $200.927   $200.93   $200.95   $200.90  
  Purchase #4 $35.56   10.167%   $39.1754   $39.18   $39.20   $39.20  
  Purchase #5 $11.27   9.117%   $12.2975   $12.30   $12.30   $12.30  
  Purchase #6 $96.62   13.646%   $109.8048   $109.80   $109.80   $109.80  
  Purchase #7 $222.84   5.405%   $234.8845   $234.88   $234.90   $234.90  
  7 purchase totals = $806.96       $871.2564   $871.26   $871.30   $871.20