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 $61.96   6.204%   $65.804   $65.80   $65.80   $65.80  
  Purchase #2 $42.65   11.182%   $47.4191   $47.42   $47.40   $47.40  
  Purchase #3 $228.62   13.836%   $260.2519   $260.25   $260.25   $260.30  
  Purchase #4 $141.51   4.531%   $147.9218   $147.92   $147.90   $147.90  
  Purchase #5 $211.75   9.853%   $232.6137   $232.61   $232.60   $232.60  
  Purchase #6 $98.31   8.526%   $106.6919   $106.69   $106.70   $106.70  
  Purchase #7 $140.31   10.630%   $155.225   $155.23   $155.25   $155.20  
  7 purchase totals = $925.11       $1,015.9274   $1,015.92   $1,015.90   $1,015.90