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 $81.85   4.571%   $85.5914   $85.59   $85.60   $85.60  
  Purchase #2 $153.99   13.387%   $174.6046   $174.60   $174.60   $174.60  
  Purchase #3 $116.43   6.575%   $124.0853   $124.09   $124.10   $124.10  
  Purchase #4 $198.41   6.280%   $210.8701   $210.87   $210.85   $210.90  
  Purchase #5 $106.77   11.494%   $119.0421   $119.04   $119.05   $119.00  
  Purchase #6 $110.84   7.558%   $119.2173   $119.22   $119.20   $119.20  
  Purchase #7 $120.50   7.581%   $129.6351   $129.64   $129.65   $129.60  
  7 purchase totals = $888.79       $963.0459   $963.05   $963.05   $963.00