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 $154.26   13.788%   $175.5294   $175.53   $175.55   $175.50  
  Purchase #2 $78.36   10.271%   $86.4084   $86.41   $86.40   $86.40  
  Purchase #3 $145.61   11.390%   $162.195   $162.20   $162.20   $162.20  
  Purchase #4 $244.98   11.668%   $273.5643   $273.56   $273.55   $273.60  
  Purchase #5 $140.55   9.432%   $153.8067   $153.81   $153.80   $153.80  
  Purchase #6 $58.57   4.179%   $61.0176   $61.02   $61.00   $61.00  
  Purchase #7 $24.88   13.761%   $28.3037   $28.30   $28.30   $28.30  
  7 purchase totals = $847.21       $940.8251   $940.83   $940.80   $940.80