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 $53.93   8.179%   $58.3409   $58.34   $58.35   $58.30  
  Purchase #2 $155.49   11.230%   $172.9515   $172.95   $172.95   $173.00  
  Purchase #3 $103.78   7.675%   $111.7451   $111.75   $111.75   $111.70  
  Purchase #4 $243.57   9.439%   $266.5606   $266.56   $266.55   $266.60  
  Purchase #5 $147.92   8.179%   $160.0184   $160.02   $160.00   $160.00  
  Purchase #6 $164.36   11.668%   $183.5375   $183.54   $183.55   $183.50  
  Purchase #7 $135.69   7.702%   $146.1408   $146.14   $146.15   $146.10  
  7 purchase totals = $1,004.74       $1,099.2948   $1,099.30   $1,099.30   $1,099.20