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 $195.84   5.542%   $206.6935   $206.69   $206.70   $206.70  
  Purchase #2 $36.64   6.822%   $39.1396   $39.14   $39.15   $39.10  
  Purchase #3 $163.62   10.340%   $180.5383   $180.54   $180.55   $180.50  
  Purchase #4 $113.35   11.683%   $126.5927   $126.59   $126.60   $126.60  
  Purchase #5 $202.63   13.416%   $229.8148   $229.81   $229.80   $229.80  
  Purchase #6 $96.65   5.329%   $101.8005   $101.80   $101.80   $101.80  
  Purchase #7 $75.76   12.664%   $85.3542   $85.35   $85.35   $85.40  
  7 purchase totals = $884.49       $969.9336   $969.92   $969.95   $969.90