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 $169.52   13.749%   $192.8273   $192.83   $192.85   $192.80  
  Purchase #2 $43.90   11.722%   $49.046   $49.05   $49.05   $49.00  
  Purchase #3 $145.41   6.156%   $154.3614   $154.36   $154.35   $154.40  
  Purchase #4 $169.27   10.219%   $186.5677   $186.57   $186.55   $186.60  
  Purchase #5 $88.62   10.589%   $98.004   $98.00   $98.00   $98.00  
  Purchase #6 $155.32   13.235%   $175.8766   $175.88   $175.90   $175.90  
  Purchase #7 $24.72   12.677%   $27.8538   $27.85   $27.85   $27.90  
  7 purchase totals = $796.76       $884.5368   $884.54   $884.55   $884.60