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 $59.70   10.488%   $65.9613   $65.96   $65.95   $66.00  
  Purchase #2 $239.52   5.427%   $252.5188   $252.52   $252.50   $252.50  
  Purchase #3 $143.65   6.157%   $152.4945   $152.49   $152.50   $152.50  
  Purchase #4 $155.66   12.700%   $175.4288   $175.43   $175.45   $175.40  
  Purchase #5 $30.57   11.792%   $34.1748   $34.17   $34.15   $34.20  
  Purchase #6 $8.27   5.456%   $8.7212   $8.72   $8.70   $8.70  
  Purchase #7 $198.34   4.703%   $207.6679   $207.67   $207.65   $207.70  
  7 purchase totals = $835.71       $896.9673   $896.96   $896.90   $897.00