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 $65.52   5.340%   $69.0188   $69.02   $69.00   $69.00  
  Purchase #2 $160.32   4.837%   $168.0747   $168.07   $168.05   $168.10  
  Purchase #3 $202.78   4.423%   $211.749   $211.75   $211.75   $211.70  
  Purchase #4 $42.97   13.488%   $48.7658   $48.77   $48.75   $48.80  
  Purchase #5 $75.42   9.310%   $82.4416   $82.44   $82.45   $82.40  
  Purchase #6 $162.36   10.281%   $179.0522   $179.05   $179.05   $179.10  
  Purchase #7 $34.33   11.219%   $38.1815   $38.18   $38.20   $38.20  
  7 purchase totals = $743.70       $797.2836   $797.28   $797.25   $797.30