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 $174.87   13.553%   $198.5701   $198.57   $198.55   $198.60  
  Purchase #2 $65.39   5.600%   $69.0518   $69.05   $69.05   $69.10  
  Purchase #3 $53.45   12.263%   $60.0046   $60.00   $60.00   $60.00  
  Purchase #4 $187.61   6.799%   $200.3656   $200.37   $200.35   $200.40  
  Purchase #5 $193.53   13.714%   $220.0707   $220.07   $220.05   $220.10  
  Purchase #6 $232.74   11.530%   $259.5749   $259.57   $259.55   $259.60  
  Purchase #7 $44.37   4.773%   $46.4878   $46.49   $46.50   $46.50  
  7 purchase totals = $951.96       $1,054.1255   $1,054.12   $1,054.05   $1,054.30