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 $126.48   8.116%   $136.7451   $136.75   $136.75   $136.70  
  Purchase #2 $88.81   5.468%   $93.6661   $93.67   $93.65   $93.70  
  Purchase #3 $218.96   12.170%   $245.6074   $245.61   $245.60   $245.60  
  Purchase #4 $183.62   10.330%   $202.5879   $202.59   $202.60   $202.60  
  Purchase #5 $242.36   7.723%   $261.0775   $261.08   $261.10   $261.10  
  Purchase #6 $61.51   3.208%   $63.4832   $63.48   $63.50   $63.50  
  Purchase #7 $41.65   10.391%   $45.9779   $45.98   $46.00   $46.00  
  7 purchase totals = $963.39       $1,049.1451   $1,049.16   $1,049.20   $1,049.20