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 $209.45   7.717%   $225.6133   $225.61   $225.60   $225.60  
  Purchase #2 $96.67   8.285%   $104.6791   $104.68   $104.70   $104.70  
  Purchase #3 $227.52   4.704%   $238.2225   $238.22   $238.20   $238.20  
  Purchase #4 $116.91   11.344%   $130.1723   $130.17   $130.15   $130.20  
  Purchase #5 $46.44   6.242%   $49.3388   $49.34   $49.35   $49.30  
  Purchase #6 $62.27   3.465%   $64.4277   $64.43   $64.45   $64.40  
  Purchase #7 $155.82   13.305%   $176.5519   $176.55   $176.55   $176.60  
  7 purchase totals = $915.08       $989.0056   $989.00   $989.00   $989.00