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 $162.98   13.676%   $185.2691   $185.27   $185.25   $185.30  
  Purchase #2 $174.67   3.303%   $180.4394   $180.44   $180.45   $180.40  
  Purchase #3 $195.92   13.220%   $221.8206   $221.82   $221.80   $221.80  
  Purchase #4 $10.29   6.625%   $10.9717   $10.97   $10.95   $11.00  
  Purchase #5 $223.92   8.850%   $243.7369   $243.74   $243.75   $243.70  
  Purchase #6 $56.98   3.509%   $58.9794   $58.98   $59.00   $59.00  
  Purchase #7 $60.45   9.603%   $66.255   $66.26   $66.25   $66.30  
  7 purchase totals = $885.21       $967.4721   $967.48   $967.45   $967.50