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 $225.97   11.529%   $252.0221   $252.02   $252.00   $252.00  
  Purchase #2 $149.47   12.670%   $168.4078   $168.41   $168.40   $168.40  
  Purchase #3 $5.32   12.129%   $5.9653   $5.97   $5.95   $6.00  
  Purchase #4 $196.39   12.239%   $220.4262   $220.43   $220.45   $220.40  
  Purchase #5 $88.96   13.808%   $101.2436   $101.24   $101.25   $101.20  
  Purchase #6 $211.76   7.613%   $227.8813   $227.88   $227.90   $227.90  
  Purchase #7 $36.35   6.353%   $38.6593   $38.66   $38.65   $38.70  
  7 purchase totals = $914.22       $1,014.6056   $1,014.61   $1,014.60   $1,014.60