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 $60.92   8.225%   $65.9307   $65.93   $65.95   $65.90  
  Purchase #2 $173.56   3.339%   $179.3552   $179.36   $179.35   $179.40  
  Purchase #3 $218.96   3.244%   $226.0631   $226.06   $226.05   $226.10  
  Purchase #4 $146.49   6.485%   $155.9899   $155.99   $156.00   $156.00  
  Purchase #5 $52.43   9.203%   $57.2551   $57.26   $57.25   $57.30  
  Purchase #6 $198.61   9.204%   $216.8901   $216.89   $216.90   $216.90  
  Purchase #7 $229.64   11.269%   $255.5181   $255.52   $255.50   $255.50  
  7 purchase totals = $1,080.61       $1,157.0022   $1,157.01   $1,157.00   $1,157.10