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 $235.44   11.725%   $263.0453   $263.05   $263.05   $263.00  
  Purchase #2 $225.93   13.615%   $256.6904   $256.69   $256.70   $256.70  
  Purchase #3 $124.94   7.333%   $134.1019   $134.10   $134.10   $134.10  
  Purchase #4 $78.57   7.190%   $84.2192   $84.22   $84.20   $84.20  
  Purchase #5 $245.77   5.523%   $259.3439   $259.34   $259.35   $259.30  
  Purchase #6 $157.94   12.417%   $177.5514   $177.55   $177.55   $177.60  
  Purchase #7 $140.52   13.420%   $159.3778   $159.38   $159.40   $159.40  
  7 purchase totals = $1,209.11       $1,334.3299   $1,334.33   $1,334.35   $1,334.30