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 $239.98   6.186%   $254.8252   $254.83   $254.85   $254.80  
  Purchase #2 $207.40   7.426%   $222.8015   $222.80   $222.80   $222.80  
  Purchase #3 $70.52   12.363%   $79.2384   $79.24   $79.25   $79.20  
  Purchase #4 $158.88   4.354%   $165.7976   $165.80   $165.80   $165.80  
  Purchase #5 $46.73   12.705%   $52.667   $52.67   $52.65   $52.70  
  Purchase #6 $149.84   10.624%   $165.759   $165.76   $165.75   $165.80  
  Purchase #7 $70.49   4.355%   $73.5598   $73.56   $73.55   $73.60  
  7 purchase totals = $943.84       $1,014.6485   $1,014.66   $1,014.65   $1,014.70