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 $114.91   8.428%   $124.5946   $124.59   $124.60   $124.60  
  Purchase #2 $83.96   11.630%   $93.7245   $93.72   $93.70   $93.70  
  Purchase #3 $23.85   7.498%   $25.6383   $25.64   $25.65   $25.60  
  Purchase #4 $244.68   3.217%   $252.5514   $252.55   $252.55   $252.60  
  Purchase #5 $64.85   13.624%   $73.6852   $73.69   $73.70   $73.70  
  Purchase #6 $193.52   8.320%   $209.6209   $209.62   $209.60   $209.60  
  Purchase #7 $7.25   3.323%   $7.4909   $7.49   $7.50   $7.50  
  7 purchase totals = $733.02       $787.3058   $787.30   $787.30   $787.30