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 $248.46   10.232%   $273.8824   $273.88   $273.90   $273.90  
  Purchase #2 $109.58   13.144%   $123.9832   $123.98   $124.00   $124.00  
  Purchase #3 $142.32   10.250%   $156.9078   $156.91   $156.90   $156.90  
  Purchase #4 $144.68   6.804%   $154.524   $154.52   $154.50   $154.50  
  Purchase #5 $46.95   11.631%   $52.4108   $52.41   $52.40   $52.40  
  Purchase #6 $230.67   7.319%   $247.5527   $247.55   $247.55   $247.60  
  Purchase #7 $224.57   12.857%   $253.443   $253.44   $253.45   $253.40  
  7 purchase totals = $1,147.23       $1,262.7039   $1,262.69   $1,262.70   $1,262.70