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 $242.42   11.210%   $269.5953   $269.60   $269.60   $269.60  
  Purchase #2 $160.46   5.520%   $169.3174   $169.32   $169.30   $169.30  
  Purchase #3 $68.43   7.210%   $73.3638   $73.36   $73.35   $73.40  
  Purchase #4 $220.67   10.253%   $243.2953   $243.30   $243.30   $243.30  
  Purchase #5 $224.86   8.721%   $244.47   $244.47   $244.45   $244.50  
  Purchase #6 $12.90   4.260%   $13.4495   $13.45   $13.45   $13.40  
  Purchase #7 $58.85   11.736%   $65.7566   $65.76   $65.75   $65.80  
  7 purchase totals = $988.59       $1,079.2479   $1,079.26   $1,079.20   $1,079.30