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 $159.69   8.651%   $173.5048   $173.50   $173.50   $173.50  
  Purchase #2 $150.43   7.691%   $161.9996   $162.00   $162.00   $162.00  
  Purchase #3 $213.91   9.796%   $234.8646   $234.86   $234.85   $234.90  
  Purchase #4 $172.99   6.493%   $184.2222   $184.22   $184.20   $184.20  
  Purchase #5 $207.59   6.272%   $220.61   $220.61   $220.60   $220.60  
  Purchase #6 $51.40   4.537%   $53.732   $53.73   $53.75   $53.70  
  Purchase #7 $210.46   12.811%   $237.422   $237.42   $237.40   $237.40  
  7 purchase totals = $1,166.47       $1,266.3552   $1,266.34   $1,266.30   $1,266.30