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 $142.77   13.194%   $161.6071   $161.61   $161.60   $161.60  
  Purchase #2 $87.72   12.311%   $98.5192   $98.52   $98.50   $98.50  
  Purchase #3 $212.67   12.753%   $239.7918   $239.79   $239.80   $239.80  
  Purchase #4 $52.27   10.330%   $57.6695   $57.67   $57.65   $57.70  
  Purchase #5 $79.82   3.525%   $82.6337   $82.63   $82.65   $82.60  
  Purchase #6 $155.70   8.671%   $169.2007   $169.20   $169.20   $169.20  
  Purchase #7 $122.72   11.470%   $136.796   $136.80   $136.80   $136.80  
  7 purchase totals = $853.67       $946.2180   $946.22   $946.20   $946.20