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 $172.27   11.275%   $191.6934   $191.69   $191.70   $191.70  
  Purchase #2 $219.31   8.816%   $238.6444   $238.64   $238.65   $238.60  
  Purchase #3 $80.26   7.466%   $86.2522   $86.25   $86.25   $86.30  
  Purchase #4 $73.45   8.268%   $79.5228   $79.52   $79.50   $79.50  
  Purchase #5 $143.37   4.225%   $149.4274   $149.43   $149.45   $149.40  
  Purchase #6 $19.72   5.576%   $20.8196   $20.82   $20.80   $20.80  
  Purchase #7 $176.26   9.458%   $192.9307   $192.93   $192.95   $192.90  
  7 purchase totals = $884.64       $959.2905   $959.28   $959.30   $959.20