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 $63.45   8.599%   $68.9061   $68.91   $68.90   $68.90  
  Purchase #2 $232.50   3.604%   $240.8793   $240.88   $240.90   $240.90  
  Purchase #3 $24.46   8.784%   $26.6086   $26.61   $26.60   $26.60  
  Purchase #4 $179.47   8.429%   $194.5975   $194.60   $194.60   $194.60  
  Purchase #5 $197.52   3.108%   $203.6589   $203.66   $203.65   $203.70  
  Purchase #6 $193.53   4.536%   $202.3085   $202.31   $202.30   $202.30  
  Purchase #7 $122.89   3.300%   $126.9454   $126.95   $126.95   $126.90  
  7 purchase totals = $1,013.82       $1,063.9043   $1,063.92   $1,063.90   $1,063.90