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 $218.25   8.468%   $236.7314   $236.73   $236.75   $236.70  
  Purchase #2 $127.60   12.352%   $143.3612   $143.36   $143.35   $143.40  
  Purchase #3 $167.78   12.724%   $189.1283   $189.13   $189.15   $189.10  
  Purchase #4 $20.56   9.743%   $22.5632   $22.56   $22.55   $22.60  
  Purchase #5 $213.94   9.182%   $233.584   $233.58   $233.60   $233.60  
  Purchase #6 $238.58   13.405%   $270.5616   $270.56   $270.55   $270.60  
  Purchase #7 $26.93   12.751%   $30.3638   $30.36   $30.35   $30.40  
  7 purchase totals = $1,013.64       $1,126.2935   $1,126.28   $1,126.30   $1,126.40