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 $124.89   8.653%   $135.6967   $135.70   $135.70   $135.70  
  Purchase #2 $139.54   8.449%   $151.3297   $151.33   $151.35   $151.30  
  Purchase #3 $144.53   5.758%   $152.852   $152.85   $152.85   $152.90  
  Purchase #4 $60.63   8.183%   $65.5914   $65.59   $65.60   $65.60  
  Purchase #5 $35.33   13.253%   $40.0123   $40.01   $40.00   $40.00  
  Purchase #6 $49.93   6.261%   $53.0561   $53.06   $53.05   $53.10  
  Purchase #7 $146.45   10.233%   $161.4362   $161.44   $161.45   $161.40  
  7 purchase totals = $701.30       $759.9744   $759.98   $760.00   $760.00