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 $63.92   4.491%   $66.7906   $66.79   $66.80   $66.80  
  Purchase #2 $228.83   3.135%   $236.0038   $236.00   $236.00   $236.00  
  Purchase #3 $109.71   11.774%   $122.6273   $122.63   $122.65   $122.60  
  Purchase #4 $169.91   5.586%   $179.4012   $179.40   $179.40   $179.40  
  Purchase #5 $101.92   3.612%   $105.6014   $105.60   $105.60   $105.60  
  Purchase #6 $224.42   7.625%   $241.532   $241.53   $241.55   $241.50  
  Purchase #7 $77.90   8.635%   $84.6267   $84.63   $84.65   $84.60  
  7 purchase totals = $976.61       $1,036.5830   $1,036.58   $1,036.65   $1,036.50