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 $134.34   6.555%   $143.146   $143.15   $143.15   $143.10  
  Purchase #2 $224.65   13.320%   $254.5734   $254.57   $254.55   $254.60  
  Purchase #3 $244.81   3.205%   $252.6562   $252.66   $252.65   $252.70  
  Purchase #4 $200.53   4.717%   $209.989   $209.99   $210.00   $210.00  
  Purchase #5 $84.60   9.136%   $92.3291   $92.33   $92.35   $92.30  
  Purchase #6 $247.58   5.797%   $261.9322   $261.93   $261.95   $261.90  
  Purchase #7 $46.60   12.683%   $52.5103   $52.51   $52.50   $52.50  
  7 purchase totals = $1,183.11       $1,267.1362   $1,267.14   $1,267.15   $1,267.10