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 $171.26   11.378%   $190.746   $190.75   $190.75   $190.70  
  Purchase #2 $202.34   9.488%   $221.538   $221.54   $221.55   $221.50  
  Purchase #3 $241.53   7.546%   $259.7559   $259.76   $259.75   $259.80  
  Purchase #4 $60.39   10.681%   $66.8403   $66.84   $66.85   $66.80  
  Purchase #5 $117.46   8.608%   $127.571   $127.57   $127.55   $127.60  
  Purchase #6 $47.34   11.416%   $52.7443   $52.74   $52.75   $52.70  
  Purchase #7 $48.28   10.692%   $53.4421   $53.44   $53.45   $53.40  
  7 purchase totals = $888.60       $972.6376   $972.64   $972.65   $972.50