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 $247.28   8.605%   $268.5584   $268.56   $268.55   $268.60  
  Purchase #2 $130.83   8.546%   $142.0107   $142.01   $142.00   $142.00  
  Purchase #3 $245.79   8.338%   $266.284   $266.28   $266.30   $266.30  
  Purchase #4 $212.38   10.649%   $234.9963   $235.00   $235.00   $235.00  
  Purchase #5 $10.40   13.126%   $11.7651   $11.77   $11.75   $11.80  
  Purchase #6 $23.44   10.315%   $25.8578   $25.86   $25.85   $25.90  
  Purchase #7 $53.37   9.466%   $58.422   $58.42   $58.40   $58.40  
  7 purchase totals = $923.49       $1,007.8943   $1,007.90   $1,007.85   $1,008.00