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 $61.96   13.683%   $70.438   $70.44   $70.45   $70.40  
  Purchase #2 $159.40   8.639%   $173.1706   $173.17   $173.15   $173.20  
  Purchase #3 $129.41   9.810%   $142.1051   $142.11   $142.10   $142.10  
  Purchase #4 $176.88   3.268%   $182.6604   $182.66   $182.65   $182.70  
  Purchase #5 $116.80   8.369%   $126.575   $126.58   $126.60   $126.60  
  Purchase #6 $96.77   5.294%   $101.893   $101.89   $101.90   $101.90  
  Purchase #7 $172.59   12.516%   $194.1914   $194.19   $194.20   $194.20  
  7 purchase totals = $913.81       $991.0335   $991.04   $991.05   $991.10