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 $247.61   8.349%   $268.283   $268.28   $268.30   $268.30  
  Purchase #2 $164.43   7.675%   $177.05   $177.05   $177.05   $177.10  
  Purchase #3 $205.59   10.456%   $227.0865   $227.09   $227.10   $227.10  
  Purchase #4 $40.84   7.463%   $43.8879   $43.89   $43.90   $43.90  
  Purchase #5 $33.45   11.127%   $37.172   $37.17   $37.15   $37.20  
  Purchase #6 $58.81   10.518%   $64.9956   $65.00   $65.00   $65.00  
  Purchase #7 $44.35   11.145%   $49.2928   $49.29   $49.30   $49.30  
  7 purchase totals = $795.08       $867.7678   $867.77   $867.80   $867.90