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 $228.78   13.642%   $259.9902   $259.99   $260.00   $260.00  
  Purchase #2 $88.30   8.687%   $95.9706   $95.97   $95.95   $96.00  
  Purchase #3 $230.92   7.688%   $248.6731   $248.67   $248.65   $248.70  
  Purchase #4 $159.71   10.144%   $175.911   $175.91   $175.90   $175.90  
  Purchase #5 $19.80   11.538%   $22.0845   $22.08   $22.10   $22.10  
  Purchase #6 $196.36   8.231%   $212.5224   $212.52   $212.50   $212.50  
  Purchase #7 $123.77   5.834%   $130.9907   $130.99   $131.00   $131.00  
  7 purchase totals = $1,047.64       $1,146.1425   $1,146.13   $1,146.10   $1,146.20