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 $52.47   13.427%   $59.5151   $59.52   $59.50   $59.50  
  Purchase #2 $83.81   11.436%   $93.3945   $93.39   $93.40   $93.40  
  Purchase #3 $220.66   7.466%   $237.1345   $237.13   $237.15   $237.10  
  Purchase #4 $60.59   11.794%   $67.736   $67.74   $67.75   $67.70  
  Purchase #5 $7.81   4.299%   $8.1458   $8.15   $8.15   $8.10  
  Purchase #6 $94.60   12.728%   $106.6407   $106.64   $106.65   $106.60  
  Purchase #7 $161.87   11.551%   $180.5676   $180.57   $180.55   $180.60  
  7 purchase totals = $681.81       $753.1342   $753.14   $753.15   $753.00