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 $48.51   11.322%   $54.0023   $54.00   $54.00   $54.00  
  Purchase #2 $192.59   6.210%   $204.5498   $204.55   $204.55   $204.50  
  Purchase #3 $239.64   11.245%   $266.5875   $266.59   $266.60   $266.60  
  Purchase #4 $56.91   13.307%   $64.483   $64.48   $64.50   $64.50  
  Purchase #5 $233.35   7.305%   $250.3962   $250.40   $250.40   $250.40  
  Purchase #6 $227.48   4.584%   $237.9077   $237.91   $237.90   $237.90  
  Purchase #7 $120.58   11.659%   $134.6384   $134.64   $134.65   $134.60  
  7 purchase totals = $1,119.06       $1,212.5649   $1,212.57   $1,212.60   $1,212.50