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 $224.90   10.741%   $249.0565   $249.06   $249.05   $249.10  
  Purchase #2 $186.93   3.356%   $193.2034   $193.20   $193.20   $193.20  
  Purchase #3 $177.52   5.107%   $186.5859   $186.59   $186.60   $186.60  
  Purchase #4 $46.38   9.854%   $50.9503   $50.95   $50.95   $51.00  
  Purchase #5 $184.43   6.475%   $196.3718   $196.37   $196.35   $196.40  
  Purchase #6 $107.63   8.759%   $117.0573   $117.06   $117.05   $117.10  
  Purchase #7 $59.71   13.366%   $67.6908   $67.69   $67.70   $67.70  
  7 purchase totals = $987.50       $1,060.9160   $1,060.92   $1,060.90   $1,061.10