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 $48.60   10.447%   $53.6772   $53.68   $53.70   $53.70  
  Purchase #2 $216.70   3.124%   $223.4697   $223.47   $223.45   $223.50  
  Purchase #3 $157.61   8.848%   $171.5553   $171.56   $171.55   $171.60  
  Purchase #4 $54.69   10.699%   $60.5413   $60.54   $60.55   $60.50  
  Purchase #5 $235.64   8.109%   $254.748   $254.75   $254.75   $254.70  
  Purchase #6 $237.82   13.151%   $269.0957   $269.10   $269.10   $269.10  
  Purchase #7 $68.66   8.193%   $74.2853   $74.29   $74.30   $74.30  
  7 purchase totals = $1,019.72       $1,107.3725   $1,107.39   $1,107.40   $1,107.40