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 $37.92   9.247%   $41.4265   $41.43   $41.45   $41.40  
  Purchase #2 $174.66   3.817%   $181.3268   $181.33   $181.35   $181.30  
  Purchase #3 $198.25   10.157%   $218.3863   $218.39   $218.40   $218.40  
  Purchase #4 $56.51   13.108%   $63.9173   $63.92   $63.90   $63.90  
  Purchase #5 $128.75   6.406%   $136.9977   $137.00   $137.00   $137.00  
  Purchase #6 $149.27   4.770%   $156.3902   $156.39   $156.40   $156.40  
  Purchase #7 $205.94   4.285%   $214.7645   $214.76   $214.75   $214.80  
  7 purchase totals = $951.30       $1,013.2093   $1,013.22   $1,013.25   $1,013.20