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 $58.81   5.236%   $61.8893   $61.89   $61.90   $61.90  
  Purchase #2 $181.77   11.360%   $202.4191   $202.42   $202.40   $202.40  
  Purchase #3 $83.89   4.531%   $87.6911   $87.69   $87.70   $87.70  
  Purchase #4 $23.89   12.861%   $26.9625   $26.96   $26.95   $27.00  
  Purchase #5 $14.72   4.671%   $15.4076   $15.41   $15.40   $15.40  
  Purchase #6 $21.72   6.185%   $23.0634   $23.06   $23.05   $23.10  
  Purchase #7 $86.53   12.391%   $97.2519   $97.25   $97.25   $97.30  
  7 purchase totals = $471.33       $514.6849   $514.68   $514.65   $514.80