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 $58.44   5.778%   $61.8167   $61.82   $61.80   $61.80  
  Purchase #2 $160.99   11.349%   $179.2608   $179.26   $179.25   $179.30  
  Purchase #3 $138.87   6.285%   $147.598   $147.60   $147.60   $147.60  
  Purchase #4 $232.36   3.392%   $240.2417   $240.24   $240.25   $240.20  
  Purchase #5 $164.85   8.596%   $179.0205   $179.02   $179.00   $179.00  
  Purchase #6 $48.64   4.203%   $50.6843   $50.68   $50.70   $50.70  
  Purchase #7 $46.50   8.457%   $50.4325   $50.43   $50.45   $50.40  
  7 purchase totals = $850.65       $909.0545   $909.05   $909.05   $909.00