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 $96.84   5.870%   $102.5245   $102.52   $102.50   $102.50  
  Purchase #2 $66.84   9.753%   $73.3589   $73.36   $73.35   $73.40  
  Purchase #3 $24.44   8.822%   $26.5961   $26.60   $26.60   $26.60  
  Purchase #4 $137.49   4.779%   $144.0606   $144.06   $144.05   $144.10  
  Purchase #5 $225.26   11.548%   $251.273   $251.27   $251.25   $251.30  
  Purchase #6 $237.48   6.135%   $252.0494   $252.05   $252.05   $252.00  
  Purchase #7 $59.60   6.132%   $63.2547   $63.25   $63.25   $63.30  
  7 purchase totals = $847.95       $913.1172   $913.11   $913.05   $913.20