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 $139.63   10.257%   $153.9518   $153.95   $153.95   $154.00  
  Purchase #2 $115.99   8.476%   $125.8213   $125.82   $125.80   $125.80  
  Purchase #3 $120.64   5.138%   $126.8385   $126.84   $126.85   $126.80  
  Purchase #4 $139.26   12.542%   $156.726   $156.73   $156.75   $156.70  
  Purchase #5 $47.31   12.798%   $53.3647   $53.36   $53.35   $53.40  
  Purchase #6 $96.88   9.234%   $105.8259   $105.83   $105.85   $105.80  
  Purchase #7 $226.59   11.192%   $251.95   $251.95   $251.95   $252.00  
  7 purchase totals = $886.30       $974.4782   $974.48   $974.50   $974.50