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 $84.28   10.200%   $92.8766   $92.88   $92.90   $92.90  
  Purchase #2 $161.79   13.519%   $183.6624   $183.66   $183.65   $183.70  
  Purchase #3 $248.62   6.249%   $264.1563   $264.16   $264.15   $264.20  
  Purchase #4 $118.70   11.539%   $132.3968   $132.40   $132.40   $132.40  
  Purchase #5 $221.87   7.595%   $238.721   $238.72   $238.70   $238.70  
  Purchase #6 $108.83   11.167%   $120.983   $120.98   $121.00   $121.00  
  Purchase #7 $125.32   8.373%   $135.813   $135.81   $135.80   $135.80  
  7 purchase totals = $1,069.41       $1,168.6091   $1,168.61   $1,168.60   $1,168.70