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 $60.49   8.465%   $65.6105   $65.61   $65.60   $65.60  
  Purchase #2 $109.33   12.415%   $122.9033   $122.90   $122.90   $122.90  
  Purchase #3 $201.97   8.746%   $219.6343   $219.63   $219.65   $219.60  
  Purchase #4 $75.57   5.394%   $79.6462   $79.65   $79.65   $79.60  
  Purchase #5 $241.30   11.373%   $268.743   $268.74   $268.75   $268.70  
  Purchase #6 $9.61   7.354%   $10.3167   $10.32   $10.30   $10.30  
  Purchase #7 $201.82   6.743%   $215.4287   $215.43   $215.45   $215.40  
  7 purchase totals = $900.09       $982.2827   $982.28   $982.30   $982.10