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 $236.99   12.462%   $266.5237   $266.52   $266.50   $266.50  
  Purchase #2 $220.68   11.338%   $245.7007   $245.70   $245.70   $245.70  
  Purchase #3 $137.61   4.489%   $143.7873   $143.79   $143.80   $143.80  
  Purchase #4 $61.40   7.873%   $66.234   $66.23   $66.25   $66.20  
  Purchase #5 $115.78   10.857%   $128.3502   $128.35   $128.35   $128.40  
  Purchase #6 $105.74   9.837%   $116.1416   $116.14   $116.15   $116.10  
  Purchase #7 $179.62   7.462%   $193.0232   $193.02   $193.00   $193.00  
  7 purchase totals = $1,057.82       $1,159.7607   $1,159.75   $1,159.75   $1,159.70