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 $60.75   8.619%   $65.986   $65.99   $66.00   $66.00  
  Purchase #2 $164.79   5.140%   $173.2602   $173.26   $173.25   $173.30  
  Purchase #3 $206.40   11.202%   $229.5209   $229.52   $229.50   $229.50  
  Purchase #4 $112.64   10.474%   $124.4379   $124.44   $124.45   $124.40  
  Purchase #5 $69.63   6.310%   $74.0237   $74.02   $74.00   $74.00  
  Purchase #6 $95.48   8.559%   $103.6521   $103.65   $103.65   $103.70  
  Purchase #7 $98.93   6.168%   $105.032   $105.03   $105.05   $105.00  
  7 purchase totals = $808.62       $875.9128   $875.91   $875.90   $875.90