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 $166.34   12.474%   $187.0893   $187.09   $187.10   $187.10  
  Purchase #2 $111.26   5.477%   $117.3537   $117.35   $117.35   $117.40  
  Purchase #3 $157.62   12.395%   $177.157   $177.16   $177.15   $177.20  
  Purchase #4 $236.34   13.451%   $268.1301   $268.13   $268.15   $268.10  
  Purchase #5 $166.68   12.155%   $186.94   $186.94   $186.95   $186.90  
  Purchase #6 $31.62   8.105%   $34.1828   $34.18   $34.20   $34.20  
  Purchase #7 $116.70   6.133%   $123.8572   $123.86   $123.85   $123.90  
  7 purchase totals = $986.56       $1,094.7101   $1,094.71   $1,094.75   $1,094.80