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 $228.80   10.569%   $252.9819   $252.98   $253.00   $253.00  
  Purchase #2 $127.37   5.556%   $134.4467   $134.45   $134.45   $134.40  
  Purchase #3 $248.85   4.547%   $260.1652   $260.17   $260.15   $260.20  
  Purchase #4 $65.31   8.343%   $70.7588   $70.76   $70.75   $70.80  
  Purchase #5 $150.55   11.167%   $167.3619   $167.36   $167.35   $167.40  
  Purchase #6 $46.72   11.688%   $52.1806   $52.18   $52.20   $52.20  
  Purchase #7 $28.82   3.246%   $29.7555   $29.76   $29.75   $29.80  
  7 purchase totals = $896.42       $967.6506   $967.66   $967.65   $967.80