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 $61.73   8.185%   $66.7826   $66.78   $66.80   $66.80  
  Purchase #2 $32.73   3.280%   $33.8035   $33.80   $33.80   $33.80  
  Purchase #3 $120.85   3.428%   $124.9927   $124.99   $125.00   $125.00  
  Purchase #4 $62.81   4.347%   $65.5404   $65.54   $65.55   $65.50  
  Purchase #5 $183.35   3.722%   $190.1743   $190.17   $190.15   $190.20  
  Purchase #6 $16.45   12.671%   $18.5344   $18.53   $18.55   $18.50  
  Purchase #7 $216.97   9.167%   $236.8596   $236.86   $236.85   $236.90  
  7 purchase totals = $694.89       $736.6875   $736.67   $736.70   $736.70