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 $131.65   10.149%   $145.0112   $145.01   $145.00   $145.00  
  Purchase #2 $87.26   8.395%   $94.5855   $94.59   $94.60   $94.60  
  Purchase #3 $186.72   7.513%   $200.7483   $200.75   $200.75   $200.70  
  Purchase #4 $171.51   6.683%   $182.972   $182.97   $182.95   $183.00  
  Purchase #5 $116.89   9.139%   $127.5726   $127.57   $127.55   $127.60  
  Purchase #6 $188.61   6.567%   $200.996   $201.00   $201.00   $201.00  
  Purchase #7 $37.95   4.288%   $39.5773   $39.58   $39.60   $39.60  
  7 purchase totals = $920.59       $991.4629   $991.47   $991.45   $991.50