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 $162.60   12.552%   $183.0096   $183.01   $183.00   $183.00  
  Purchase #2 $196.87   7.789%   $212.2042   $212.20   $212.20   $212.20  
  Purchase #3 $190.38   3.223%   $196.5159   $196.52   $196.50   $196.50  
  Purchase #4 $156.81   5.255%   $165.0504   $165.05   $165.05   $165.10  
  Purchase #5 $99.62   8.553%   $108.1405   $108.14   $108.15   $108.10  
  Purchase #6 $68.74   5.738%   $72.6843   $72.68   $72.70   $72.70  
  Purchase #7 $246.56   9.192%   $269.2238   $269.22   $269.20   $269.20  
  7 purchase totals = $1,121.58       $1,206.8287   $1,206.82   $1,206.80   $1,206.80