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 $53.50   8.355%   $57.9699   $57.97   $57.95   $58.00  
  Purchase #2 $122.25   8.385%   $132.5007   $132.50   $132.50   $132.50  
  Purchase #3 $212.67   12.421%   $239.0857   $239.09   $239.10   $239.10  
  Purchase #4 $246.32   9.480%   $269.6711   $269.67   $269.65   $269.70  
  Purchase #5 $108.75   5.638%   $114.8813   $114.88   $114.90   $114.90  
  Purchase #6 $67.70   5.252%   $71.2556   $71.26   $71.25   $71.30  
  Purchase #7 $85.51   12.272%   $96.0038   $96.00   $96.00   $96.00  
  7 purchase totals = $896.70       $981.3681   $981.37   $981.35   $981.50