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 $188.28   6.595%   $200.6971   $200.70   $200.70   $200.70  
  Purchase #2 $166.54   3.402%   $172.2057   $172.21   $172.20   $172.20  
  Purchase #3 $224.80   11.398%   $250.4227   $250.42   $250.40   $250.40  
  Purchase #4 $169.80   9.540%   $185.9989   $186.00   $186.00   $186.00  
  Purchase #5 $221.92   9.425%   $242.836   $242.84   $242.85   $242.80  
  Purchase #6 $20.99   4.369%   $21.9071   $21.91   $21.90   $21.90  
  Purchase #7 $65.60   4.608%   $68.6228   $68.62   $68.60   $68.60  
  7 purchase totals = $1,057.93       $1,142.6903   $1,142.70   $1,142.65   $1,142.60