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 $191.45   10.212%   $211.0009   $211.00   $211.00   $211.00  
  Purchase #2 $61.27   12.761%   $69.0887   $69.09   $69.10   $69.10  
  Purchase #3 $105.25   4.396%   $109.8768   $109.88   $109.90   $109.90  
  Purchase #4 $211.71   8.118%   $228.8966   $228.90   $228.90   $228.90  
  Purchase #5 $166.93   9.171%   $182.2392   $182.24   $182.25   $182.20  
  Purchase #6 $50.28   3.202%   $51.89   $51.89   $51.90   $51.90  
  Purchase #7 $100.52   7.593%   $108.1525   $108.15   $108.15   $108.20  
  7 purchase totals = $887.41       $961.1447   $961.15   $961.20   $961.20