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 $74.80   11.294%   $83.2479   $83.25   $83.25   $83.20  
  Purchase #2 $171.28   3.124%   $176.6308   $176.63   $176.65   $176.60  
  Purchase #3 $6.41   8.418%   $6.9496   $6.95   $6.95   $6.90  
  Purchase #4 $86.59   11.152%   $96.2465   $96.25   $96.25   $96.20  
  Purchase #5 $60.62   7.444%   $65.1326   $65.13   $65.15   $65.10  
  Purchase #6 $186.84   8.152%   $202.0712   $202.07   $202.05   $202.10  
  Purchase #7 $112.49   6.194%   $119.4576   $119.46   $119.45   $119.50  
  7 purchase totals = $699.03       $749.7362   $749.74   $749.75   $749.60