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 $151.26   10.196%   $166.6825   $166.68   $166.70   $166.70  
  Purchase #2 $69.50   4.599%   $72.6963   $72.70   $72.70   $72.70  
  Purchase #3 $196.60   5.107%   $206.6404   $206.64   $206.65   $206.60  
  Purchase #4 $49.45   4.533%   $51.6916   $51.69   $51.70   $51.70  
  Purchase #5 $31.89   9.607%   $34.9537   $34.95   $34.95   $35.00  
  Purchase #6 $84.42   7.627%   $90.8587   $90.86   $90.85   $90.90  
  Purchase #7 $81.51   8.435%   $88.3854   $88.39   $88.40   $88.40  
  7 purchase totals = $664.63       $711.9086   $711.91   $711.95   $712.00