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 $246.99   7.754%   $266.1416   $266.14   $266.15   $266.10  
  Purchase #2 $63.42   7.135%   $67.945   $67.95   $67.95   $67.90  
  Purchase #3 $101.81   5.747%   $107.661   $107.66   $107.65   $107.70  
  Purchase #4 $243.61   9.623%   $267.0526   $267.05   $267.05   $267.10  
  Purchase #5 $212.86   9.286%   $232.6262   $232.63   $232.65   $232.60  
  Purchase #6 $168.29   12.610%   $189.5114   $189.51   $189.50   $189.50  
  Purchase #7 $34.87   9.771%   $38.2771   $38.28   $38.30   $38.30  
  7 purchase totals = $1,071.85       $1,169.2149   $1,169.22   $1,169.25   $1,169.20