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 $247.96   4.677%   $259.5571   $259.56   $259.55   $259.60  
  Purchase #2 $234.41   11.846%   $262.1782   $262.18   $262.20   $262.20  
  Purchase #3 $195.65   8.769%   $212.8065   $212.81   $212.80   $212.80  
  Purchase #4 $99.70   3.709%   $103.3979   $103.40   $103.40   $103.40  
  Purchase #5 $48.80   10.858%   $54.0987   $54.10   $54.10   $54.10  
  Purchase #6 $94.95   11.645%   $106.0069   $106.01   $106.00   $106.00  
  Purchase #7 $241.47   9.740%   $264.9892   $264.99   $265.00   $265.00  
  7 purchase totals = $1,162.94       $1,263.0345   $1,263.05   $1,263.05   $1,263.10