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 $9.77   12.797%   $11.0203   $11.02   $11.00   $11.00  
  Purchase #2 $226.71   8.743%   $246.5313   $246.53   $246.55   $246.50  
  Purchase #3 $41.53   12.346%   $46.6573   $46.66   $46.65   $46.70  
  Purchase #4 $67.52   3.492%   $69.8778   $69.88   $69.90   $69.90  
  Purchase #5 $87.52   3.419%   $90.5123   $90.51   $90.50   $90.50  
  Purchase #6 $42.53   3.863%   $44.1729   $44.17   $44.15   $44.20  
  Purchase #7 $210.59   5.842%   $222.8927   $222.89   $222.90   $222.90  
  7 purchase totals = $686.17       $731.6646   $731.66   $731.65   $731.70