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 $181.81   9.236%   $198.602   $198.60   $198.60   $198.60  
  Purchase #2 $56.32   11.791%   $62.9607   $62.96   $62.95   $63.00  
  Purchase #3 $27.33   4.247%   $28.4907   $28.49   $28.50   $28.50  
  Purchase #4 $241.37   3.874%   $250.7207   $250.72   $250.70   $250.70  
  Purchase #5 $76.67   5.251%   $80.6959   $80.70   $80.70   $80.70  
  Purchase #6 $139.59   11.852%   $156.1342   $156.13   $156.15   $156.10  
  Purchase #7 $159.87   6.292%   $169.929   $169.93   $169.95   $169.90  
  7 purchase totals = $882.96       $947.5332   $947.53   $947.55   $947.50