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 $126.65   8.199%   $137.034   $137.03   $137.05   $137.00  
  Purchase #2 $77.82   13.727%   $88.5024   $88.50   $88.50   $88.50  
  Purchase #3 $48.93   7.567%   $52.6325   $52.63   $52.65   $52.60  
  Purchase #4 $80.25   12.641%   $90.3944   $90.39   $90.40   $90.40  
  Purchase #5 $162.48   11.239%   $180.7411   $180.74   $180.75   $180.70  
  Purchase #6 $178.27   9.322%   $194.8883   $194.89   $194.90   $194.90  
  Purchase #7 $93.45   5.265%   $98.3701   $98.37   $98.35   $98.40  
  7 purchase totals = $767.85       $842.5628   $842.55   $842.60   $842.50