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 $234.69   11.677%   $262.0948   $262.09   $262.10   $262.10  
  Purchase #2 $142.39   5.303%   $149.9409   $149.94   $149.95   $149.90  
  Purchase #3 $146.52   8.160%   $158.476   $158.48   $158.50   $158.50  
  Purchase #4 $225.68   6.245%   $239.7737   $239.77   $239.75   $239.80  
  Purchase #5 $73.67   10.594%   $81.4746   $81.47   $81.45   $81.50  
  Purchase #6 $174.53   12.473%   $196.2991   $196.30   $196.30   $196.30  
  Purchase #7 $33.32   8.152%   $36.0362   $36.04   $36.05   $36.00  
  7 purchase totals = $1,030.80       $1,124.0953   $1,124.09   $1,124.10   $1,124.10