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 $29.77   12.623%   $33.5279   $33.53   $33.55   $33.50  
  Purchase #2 $155.92   8.433%   $169.0687   $169.07   $169.05   $169.10  
  Purchase #3 $31.45   4.280%   $32.7961   $32.80   $32.80   $32.80  
  Purchase #4 $46.35   7.293%   $49.7303   $49.73   $49.75   $49.70  
  Purchase #5 $201.29   10.681%   $222.7898   $222.79   $222.80   $222.80  
  Purchase #6 $157.73   11.595%   $176.0188   $176.02   $176.00   $176.00  
  Purchase #7 $59.97   13.210%   $67.892   $67.89   $67.90   $67.90  
  7 purchase totals = $682.48       $751.8236   $751.83   $751.85   $751.80