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 $59.65   8.794%   $64.8956   $64.90   $64.90   $64.90  
  Purchase #2 $191.92   4.361%   $200.2896   $200.29   $200.30   $200.30  
  Purchase #3 $22.77   12.484%   $25.6126   $25.61   $25.60   $25.60  
  Purchase #4 $207.75   9.143%   $226.7446   $226.74   $226.75   $226.70  
  Purchase #5 $214.46   7.670%   $230.9091   $230.91   $230.90   $230.90  
  Purchase #6 $182.58   5.399%   $192.4375   $192.44   $192.45   $192.40  
  Purchase #7 $189.76   6.701%   $202.4758   $202.48   $202.50   $202.50  
  7 purchase totals = $1,068.89       $1,143.3648   $1,143.37   $1,143.40   $1,143.30