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 $57.53   3.233%   $59.3899   $59.39   $59.40   $59.40  
  Purchase #2 $184.85   4.520%   $193.2052   $193.21   $193.20   $193.20  
  Purchase #3 $52.93   3.384%   $54.7212   $54.72   $54.70   $54.70  
  Purchase #4 $112.91   3.354%   $116.697   $116.70   $116.70   $116.70  
  Purchase #5 $76.66   7.508%   $82.4156   $82.42   $82.40   $82.40  
  Purchase #6 $129.59   11.541%   $144.546   $144.55   $144.55   $144.50  
  Purchase #7 $192.31   6.471%   $204.7544   $204.75   $204.75   $204.80  
  7 purchase totals = $806.78       $855.7293   $855.74   $855.70   $855.70