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 $50.83   13.386%   $57.6341   $57.63   $57.65   $57.60  
  Purchase #2 $172.49   4.529%   $180.3021   $180.30   $180.30   $180.30  
  Purchase #3 $163.97   5.439%   $172.8883   $172.89   $172.90   $172.90  
  Purchase #4 $53.79   13.169%   $60.8736   $60.87   $60.85   $60.90  
  Purchase #5 $228.45   13.863%   $260.12   $260.12   $260.10   $260.10  
  Purchase #6 $20.50   11.644%   $22.887   $22.89   $22.90   $22.90  
  Purchase #7 $206.75   12.109%   $231.7854   $231.79   $231.80   $231.80  
  7 purchase totals = $896.78       $986.4905   $986.49   $986.50   $986.50