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 $110.59   13.404%   $125.4135   $125.41   $125.40   $125.40  
  Purchase #2 $208.35   8.740%   $226.5598   $226.56   $226.55   $226.60  
  Purchase #3 $117.89   10.710%   $130.516   $130.52   $130.50   $130.50  
  Purchase #4 $157.58   5.385%   $166.0657   $166.07   $166.05   $166.10  
  Purchase #5 $145.66   9.678%   $159.757   $159.76   $159.75   $159.80  
  Purchase #6 $77.92   10.517%   $86.1148   $86.11   $86.10   $86.10  
  Purchase #7 $152.37   9.298%   $166.5374   $166.54   $166.55   $166.50  
  7 purchase totals = $970.36       $1,060.9642   $1,060.97   $1,060.90   $1,061.00