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 $174.48   13.286%   $197.6614   $197.66   $197.65   $197.70  
  Purchase #2 $183.43   11.558%   $204.6308   $204.63   $204.65   $204.60  
  Purchase #3 $242.76   11.378%   $270.3812   $270.38   $270.40   $270.40  
  Purchase #4 $26.96   11.130%   $29.9606   $29.96   $29.95   $30.00  
  Purchase #5 $177.85   10.245%   $196.0707   $196.07   $196.05   $196.10  
  Purchase #6 $194.41   4.805%   $203.7514   $203.75   $203.75   $203.80  
  Purchase #7 $34.79   10.638%   $38.491   $38.49   $38.50   $38.50  
  7 purchase totals = $1,034.68       $1,140.9471   $1,140.94   $1,140.95   $1,141.10