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 $163.95   8.174%   $177.3513   $177.35   $177.35   $177.40  
  Purchase #2 $96.87   13.441%   $109.8903   $109.89   $109.90   $109.90  
  Purchase #3 $241.59   8.674%   $262.5455   $262.55   $262.55   $262.50  
  Purchase #4 $196.32   3.593%   $203.3738   $203.37   $203.35   $203.40  
  Purchase #5 $138.78   10.785%   $153.7474   $153.75   $153.75   $153.70  
  Purchase #6 $28.71   10.758%   $31.7986   $31.80   $31.80   $31.80  
  Purchase #7 $168.37   10.242%   $185.6145   $185.61   $185.60   $185.60  
  7 purchase totals = $1,034.59       $1,124.3214   $1,124.32   $1,124.30   $1,124.30