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 $73.71   12.309%   $82.783   $82.78   $82.80   $82.80  
  Purchase #2 $204.52   9.342%   $223.6263   $223.63   $223.65   $223.60  
  Purchase #3 $124.83   4.360%   $130.2726   $130.27   $130.25   $130.30  
  Purchase #4 $72.36   7.330%   $77.664   $77.66   $77.65   $77.70  
  Purchase #5 $103.32   10.153%   $113.8101   $113.81   $113.80   $113.80  
  Purchase #6 $226.58   6.520%   $241.353   $241.35   $241.35   $241.40  
  Purchase #7 $91.38   4.582%   $95.567   $95.57   $95.55   $95.60  
  7 purchase totals = $896.70       $965.0760   $965.07   $965.05   $965.20