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 $62.97   9.142%   $68.7267   $68.73   $68.75   $68.70  
  Purchase #2 $108.83   7.184%   $116.6483   $116.65   $116.65   $116.60  
  Purchase #3 $234.77   5.782%   $248.3444   $248.34   $248.35   $248.30  
  Purchase #4 $225.92   3.760%   $234.4146   $234.41   $234.40   $234.40  
  Purchase #5 $141.59   11.190%   $157.4339   $157.43   $157.45   $157.40  
  Purchase #6 $9.81   12.466%   $11.0329   $11.03   $11.05   $11.00  
  Purchase #7 $163.30   11.117%   $181.4541   $181.45   $181.45   $181.50  
  7 purchase totals = $947.19       $1,018.0549   $1,018.04   $1,018.10   $1,017.90