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 $161.52   3.332%   $166.9018   $166.90   $166.90   $166.90  
  Purchase #2 $238.34   10.204%   $262.6602   $262.66   $262.65   $262.70  
  Purchase #3 $106.65   12.278%   $119.7445   $119.74   $119.75   $119.70  
  Purchase #4 $223.36   6.337%   $237.5143   $237.51   $237.50   $237.50  
  Purchase #5 $146.97   7.211%   $157.568   $157.57   $157.55   $157.60  
  Purchase #6 $49.53   13.112%   $56.0244   $56.02   $56.00   $56.00  
  Purchase #7 $86.81   12.176%   $97.38   $97.38   $97.40   $97.40  
  7 purchase totals = $1,013.18       $1,097.7932   $1,097.78   $1,097.75   $1,097.80