Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $153.60   4.707%   $160.83   $160.83   $160.85   $160.80  
  Purchase #2 $159.34   8.452%   $172.8074   $172.81   $172.80   $172.80  
  Purchase #3 $107.61   7.704%   $115.9003   $115.90   $115.90   $115.90  
  Purchase #4 $139.90   3.455%   $144.7335   $144.73   $144.75   $144.70  
  Purchase #5 $32.83   13.276%   $37.1885   $37.19   $37.20   $37.20  
  Purchase #6 $130.30   12.827%   $147.0136   $147.01   $147.00   $147.00  
  Purchase #7 $55.53   5.251%   $58.4459   $58.45   $58.45   $58.40  
  7 purchase totals = $779.11       $836.9192   $836.92   $836.95   $836.80