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 $61.76   8.251%   $66.8558   $66.86   $66.85   $66.90  
  Purchase #2 $20.82   4.762%   $21.8114   $21.81   $21.80   $21.80  
  Purchase #3 $33.89   3.452%   $35.0599   $35.06   $35.05   $35.10  
  Purchase #4 $126.58   3.323%   $130.7863   $130.79   $130.80   $130.80  
  Purchase #5 $46.92   11.592%   $52.359   $52.36   $52.35   $52.40  
  Purchase #6 $97.40   8.619%   $105.7949   $105.79   $105.80   $105.80  
  Purchase #7 $67.55   3.556%   $69.9521   $69.95   $69.95   $70.00  
  7 purchase totals = $454.92       $482.6194   $482.62   $482.60   $482.80