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 $61.68   6.154%   $65.4758   $65.48   $65.50   $65.50  
  Purchase #2 $219.93   11.511%   $245.2461   $245.25   $245.25   $245.20  
  Purchase #3 $81.26   4.454%   $84.8793   $84.88   $84.90   $84.90  
  Purchase #4 $149.87   11.222%   $166.6884   $166.69   $166.70   $166.70  
  Purchase #5 $227.70   6.536%   $242.5825   $242.58   $242.60   $242.60  
  Purchase #6 $250.29   7.687%   $269.5298   $269.53   $269.55   $269.50  
  Purchase #7 $20.72   7.402%   $22.2537   $22.25   $22.25   $22.30  
  7 purchase totals = $1,011.45       $1,096.6556   $1,096.66   $1,096.75   $1,096.70