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 $61.38   8.637%   $66.6814   $66.68   $66.70   $66.70  
  Purchase #2 $249.89   5.795%   $264.3711   $264.37   $264.35   $264.40  
  Purchase #3 $5.54   4.743%   $5.8028   $5.80   $5.80   $5.80  
  Purchase #4 $140.28   11.511%   $156.4276   $156.43   $156.45   $156.40  
  Purchase #5 $62.76   7.171%   $67.2605   $67.26   $67.25   $67.30  
  Purchase #6 $111.65   6.549%   $118.962   $118.96   $118.95   $119.00  
  Purchase #7 $24.58   8.821%   $26.7482   $26.75   $26.75   $26.70  
  7 purchase totals = $656.08       $706.2536   $706.25   $706.25   $706.30