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 $204.48   6.163%   $217.0821   $217.08   $217.10   $217.10  
  Purchase #2 $152.77   10.451%   $168.736   $168.74   $168.75   $168.70  
  Purchase #3 $86.99   11.127%   $96.6694   $96.67   $96.65   $96.70  
  Purchase #4 $14.49   10.333%   $15.9873   $15.99   $16.00   $16.00  
  Purchase #5 $238.69   11.236%   $265.5092   $265.51   $265.50   $265.50  
  Purchase #6 $185.88   7.432%   $199.6946   $199.69   $199.70   $199.70  
  Purchase #7 $63.87   12.621%   $71.931   $71.93   $71.95   $71.90  
  7 purchase totals = $947.17       $1,035.6096   $1,035.61   $1,035.65   $1,035.60