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 $228.86   11.274%   $254.6617   $254.66   $254.65   $254.70  
  Purchase #2 $178.28   10.664%   $197.2918   $197.29   $197.30   $197.30  
  Purchase #3 $5.70   4.330%   $5.9468   $5.95   $5.95   $5.90  
  Purchase #4 $64.78   3.246%   $66.8828   $66.88   $66.90   $66.90  
  Purchase #5 $23.53   8.477%   $25.5246   $25.52   $25.50   $25.50  
  Purchase #6 $176.56   4.467%   $184.4469   $184.45   $184.45   $184.40  
  Purchase #7 $239.37   3.459%   $247.6498   $247.65   $247.65   $247.60  
  7 purchase totals = $917.08       $982.4044   $982.40   $982.40   $982.30