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 $178.95   9.855%   $196.5855   $196.59   $196.60   $196.60  
  Purchase #2 $116.52   8.124%   $125.9861   $125.99   $126.00   $126.00  
  Purchase #3 $116.50   7.305%   $125.0103   $125.01   $125.00   $125.00  
  Purchase #4 $218.51   3.735%   $226.6713   $226.67   $226.65   $226.70  
  Purchase #5 $65.48   11.578%   $73.0613   $73.06   $73.05   $73.10  
  Purchase #6 $172.52   6.356%   $183.4854   $183.49   $183.50   $183.50  
  Purchase #7 $53.27   6.789%   $56.8865   $56.89   $56.90   $56.90  
  7 purchase totals = $921.75       $987.6864   $987.70   $987.70   $987.80