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 $198.68   6.272%   $211.1412   $211.14   $211.15   $211.10  
  Purchase #2 $156.83   8.218%   $169.7183   $169.72   $169.70   $169.70  
  Purchase #3 $203.92   5.626%   $215.3925   $215.39   $215.40   $215.40  
  Purchase #4 $135.63   11.836%   $151.6832   $151.68   $151.70   $151.70  
  Purchase #5 $67.59   4.783%   $70.8228   $70.82   $70.80   $70.80  
  Purchase #6 $44.52   13.850%   $50.686   $50.69   $50.70   $50.70  
  Purchase #7 $243.57   11.867%   $272.4745   $272.47   $272.45   $272.50  
  7 purchase totals = $1,050.74       $1,141.9185   $1,141.91   $1,141.90   $1,141.90